CHAPTER FOUR: COMPOUNDS AND THEIR BONDS Flashcards
1
Q
In nature, _________ ________ the elements on the Periodic Table are found in combination with other atoms.
Only the atoms of the ________ _______ do not combine in nature with other atoms.
A
Almost all
Noble gases
2
Q
What is a COMPOUND?
In a typical IONIC COMPOUND, one or more ____________ are transferred from the atoms of metals to atoms of ___________.
The attraction that results is called an ___________ __________.
A
A compound is a pure substance composed of two or more elements with a definite composition.
ELECTRONS, NONMETALS
IONIC BOND
3
Q
In compounds of NONMETALS, _________ bonding occurs by atoms sharing one or more ___________ electrons.
A
COVALENT bonding
VALENCE electrons
4
Q
Are COVALENT or IONIC compounds more prevalent?
A
COVALENT
5
Q
COVALENT COMPOUNDS consist of ____________ which are discrete groups of __________.
A
MOLECULES; ATOMS
6
Q
IONIC BONDS occur when atoms of one element _______________ and the atoms of another element __________________.
A
LOSE valence electrons
GAIN valence electrons
7
Q
COVALENT BONDS occur when atoms of nonmetals _______________.
A
SHARE valence electrons.
8
Q
The NOBLE GASES are so stable that they form compounds only ______________.
Why are they so stable?
A
under extreme conditions.
They have 8 valence electrons
9
Q
What is the OCTET RULE?
A
The tendency for atoms to attain a noble gas electron arrangement is known as the OCTET RULE and provides a key to our understanding of the ways in which atoms bond and form compounds.
10
Q
Describe IONIC BONDING.
A METAL atom readily loses valence electrons. In doing so, a metal atom obtains the same electron arrangement as its nearest __________ _________ (usually ____ valence electrons).
By losing electrons, a metal atom forms an _____, which has a positive charge.
A
In IONIC BONDING, ions, which have electrical charges, form when atoms lose or gain electrons to form OCTETS.
NOBLE GAS; 8
ION
11
Q
What is an IONIC CHARGE?
A
the difference between the number of protons (positive charge) and the number of electrons (negative charge)
12
Q
What are CATIONS?
A
Metals in ionic compounds lose their valence electrons to form positively charged ions called CATIONS
13
Q
A metal ion is named by its ____________ ________. Thus Mg^2+ is named the _____ _______.
A
A metal ion is named by its ELEMENT NAME.
magnesium ion
14
Q
The ionization energy of a NONMETAL atom in Group 5A, 6A or 7A is ________.
Rather than _____ electrons in an ionic compound, a NONMETAL atom ______ one or more valence electrons to attain an ______.
In doing so, a nonmetal atom obtains the same electron arrangement as its nearest _____ ______ and forms a __________- charged ion.
A
HIGH
LOSE; GAINS; OCTET
NOBLE GAS; NEGATIVELY
15
Q
A negatively charged ion, also called an _________, is named by using the first syllable of its name followed by ______
A
ANION
ide
16
Q
We can obtain the number of valence electrons of the REPRESENTATIVE ELEMENTS from the ________ ___________ on the Periodic Table.
We can also use those to determine the _____ _______ for most of the ions.
Group 1A- lose _____ electron to form ions with a _____ charge
What about the same for Group 2A, 3A?
A
GROUP NUMBERS
IONIC CHARGES
1A- lose 1 electron to form ions with a 1+ charge
2A- lose 2 electr. to form ions with a 2+ charge
3A- lose 3 electr. to form ions with a 3+ charge
17
Q
In IONIC COMPOUNDS the atoms of the elements in Group 7A ___ (gain or lose?) ___ (how many?) electron(s) to form ions with a _______ charge.
How about the elements in:
- Group 6A
- Group 5A
A
GAIN ONE electron; form ions with a 1- charge
6A- gain 2 electr. to form ions with a 2- charge
5A- gain 3 electr. to form ions with a 2- charge
18
Q
The NONMETALS of Group 4A ______ (do or do not) typically form ions.
The metals Sn and Pb in Group 4A _____ electrons to form _______ ions.
A
DO NOT
LOSE; POSITIVE
19
Q
IONIC COMPOUNDS consist of ______ and ______ ions, held together by strong attractions between the oppositely charge ions, called ________ __________.
A
POSITIVE; NEGATIVE
IONIC BONDS
20
Q
The physical and chemical properties of an ionic compound are ______ ________ ________ those of the original elements.
A
Very different from
21
Q
What accounts for the high melting points of ionic compounds?
At room temperature, ionic compounds are ________.
A
There are many strong attractions between the positive and negative ions.
SOLIDS
22
Q
What do we mean when we say “the FORMULA of an ionic compound”?
The sum of the ionic charges in the formula is always _______, which means that the ____________.
A
This indicates the number and kinds of ions that make up the ionic compound.
ZERO, which means that the total amount of positive charge is equal to the total amount of negative charge.
Ex: the formula NaCl indicates that the compound consists of one sodium ion, Na+, for every chloride ion, Cl-. Although th ions are positively or negatively charged, their ionic charges are not shown in the formula of the compound.
23
Q
Explain how SUBSCRIPTS are used in formulas of ionic compounds. Use magnesium and chlorine as an example.
A
Ex: To achieve an octet, a MG atom loses its 2 valence electrons to form Mg^ 2+. Two Cl atoms each gain one electron to form 2 Cl- ions.
The 2 Cl- ions are needed to balance the positive charge of Mg^2+. This gives the formula MgCl2 (the 2 is subscript), magnesium chloride, in which a subscript of 2 shows that 2 Cl- are needed for CHARGE BALANCE
24
Q
The subscripts in the formula of an ionic compound represent the number of ______ and ______ ions that give an overall charge of ______.
A
POSITIVE; NEGATIVE
ZERO
25
What is a FORMULA UNIT?
In the formula of an ionic compound, the _______ is written first, followed by the _____.
Ex: write the formula of the ionic compound containing Na+ and S2- ions.
A FORMULA UNIT is the lowest ratio of the ions in an ionic compound.
The CATION is written first, followed by the ANION.
Ex: write the formula of the ionic compound containing Na+ and S2- ions:
To balance the ionic charge of the S2- ion, we will need to place 2 Na+ ions in the formula. This gives the formula Na(sub)2S, which has an overall charge of zero.
26
Naming IONIC COMPOUNDS:
* metal ions
* nonmetal ions
* any compound
The name of a METAL is the same as its elemental name.
The name of a NONMETAL ION is obtained by using the first syllable of its elemental name, followed by ide.
In the name of any COMPOUND, a ______ separates the name of the metal ion from the name of the nonmetal ion.
27
How do we name IONIC COMPOUNDS containing 2 elements?
Are subscripts mentioned? Why?
In the name of an ionic compound made up of two elements, the name of the METAL ION is given first, followed by the name of the NONMETAL ION.
SUBSCRIPTS are NEVER mentioned. They are understood as a result of the charge balance of the ions in the compound.
28
What are the FOUR steps to naming ionic compounds with metals that form a single ion?
1. Identify the CATION and ANION.
2. Name the CATION by its element name.
3. Name the ANION by using the first syllable of its element name followed by ide.
4. Write the name of the CATION first and the name of the ANION second.
29
It is not as easy to determine the charge of a TRANSITION ELEMENT because they typically form two or more positive ions. They _______ electrons from the ______ energy level and sometimes from a ______ energy level as well.
This is also true for metals of REPRESENTATIVE ELEMENTS in groups ____ and ______.
LOSE electrons from the HIGHEST energy level and sometimes from a LOWER energy level as well.
Groups 4A and 5A, such as Pb, Sn and Bi
30
What is VARIABLE CHARGE?
In this case, can we predict the ionic charge from the group number?
When a metal can form two or more types of ions, it has VARIABLE CHARGE.
Ex:
* Iron has two forms Fe^2+ and Fe^3+
* Copper has two forms Cu+ and Cu2+
We CANNOT predict the ionic charge from the group number, in this case.
31
When different ions are possible, a naming system is used to identify the particular CATION. How does this work?
A Roman numeral that is equal to the ionic charge is placed in parentheses immediately after the elemental name.
Ex: Fe^2+ is iron(II) and Fe^3+ is iron(III)
32
The TRANSITION ELEMENTS form more than one positive ion except for _______, _______ and ________, which form only one ion.
zinc (Zn^2+)
cadmium (Cd^2+)
silver (Ag+)
Thus, only the elemental names of zinc, cadmium and silver are sufficient when naming their cations in ionic compounds.
33
Metals in Groups _____ and _____ also form more than one type of positive ion.
4A and 5A
Ex: lead and tin in Group 4A form cations with charges of 2+ and 4+
34
When you name an ionic compound, you need to determine if the metal is a _______ or a __________.
If it is a TRANSITION ELEMENT, you will need to use __________ as part of its name, except for ______, ________ or silver.
REPRESENTATIVE ELEMENT or a TRANSITION ELEMENT.
...use its IONIC CHARGE as a ROMAN NUMERAL...
....except for zinc, cadmium or silver.
Ex: We use CHARGE BALANCE to determine the charge of a copper cation in the ionic compound CuCl2. Because there are 2 chloride ions, each with a 1- charge, the total negative charge is 2-. To balance this, the copper ion must have a charge or 2+, or Cu^2+. To indicate the 2+ charge for the copper ion Cu^2+, we place the Roman Numeral (II) immediately after copper when naming this compound: copper (II) chloride . (see page 135-136 in text)
35
Name the FOUR steps to naming ionic compounds with VARIABLE CHARGE METALS
1. Determine the charge of the cation from the anion.
2. Name the cation by its element name and use a Roman numeral in parentheses for the charge.
3. Name the anion by using the first syllable of its element name followed by ide
4. Write the name of the cation first and the name of the anion second.
36
The formula of an IONIC COMPOUND is written from the first part of the name for the ionic compound, which is the ________ ion, and the second part of the name, which is the ________ ion.
__________ are added, as needed, to balance the charge.
METAL; NONMETAL
SUBSCRIPTS
37
What are the THREE steps to writing formulas from the name of an IONIC COMPOUND?
1. Identify the CATION and ANION
2. BALANCE the charges
3. Write the formula, cation first, using subscripts from the charge balance.
38
What is a POLYATOMIC ION?
Most polyatomic ions consist of a ______ bonded to _____ atoms
Almost all polyatomic ions are _____ with charges of ____, ______ or ______, which indicate that the group of atoms has _______________ to complete octets.
Only one common polyatomic ion, ________, has a ______ charge.
A group of atoms that has an overall IONIC CHARGE.
NONMETAL (such as phosphorus, sulfur, carbon or nitrogen) bonded to OXYGEN atoms.
ANIONS with charges of 1-, 2- or 3-...the group of atoms has gained 1, 2 or 3 ELECTRONS to complete octets.
NH(sub)4+; POSITIVE charge
39
The names of the most common POLYATOMIC IONS end in ________.
When a related ion has one less oxygen atom, the ______ ending is used for its name.
What are the 2 exceptions to this naming pattern?
ate
ite
The hydroxide ion (OH-) and cyanide ion (CN-) are exceptions.
40
Other things to know about NAMES of POLYATOMIC IONS:
* by recognizing the formulas, charges and names of the ions (in Table 4.7), you can derive the ______ ________.
* both the _____ ion and the ____ ion of a particular nonmetal have the same ionic charge.
* the HALOGENS form ____ different polyatomic ions with oxygen. The one with one more oxygen than chlorate uses the prefix ____, the one with one oxygen less than chlorite uses the prefix _____.
...you can derive the RELATED IONS
...both the ATE ion and the ITE ion
FOUR; per; hypo
41
The formula of hydrogen carbonate (or bicarbonate) is written with a ________ in front of the polyatomic formula for carbonate and decreasing the charge to _____ to give _______.
HYDROGEN; 1-; HCO(sub)3^2-
CO(sub)3^2- + H+ = HCO(sub)3-
42
Like any ion, a POLYATOMIC ION must be associated with ions of _____ ______.
The bonding between polyatomic ions and other ions is one of ________ attraction.
OPPOSITE CHARGE
ELECTRICAL
Ex: the compound SODIUM SULFATE consists of sodium ions (Na+) and sulfate ions (SO(sub)4^2-) held together by ionic bonds.
43
To write correct formulas for compounds containing POLYATOMIC IONS, we follow he same rules of CHARGE BALANCE that we use for writing formulas of SIMPLE IONIC COMPOUNDS. The total negative and positive charges must equal ______.
When more than one POLYATOMIC ION is needed for charge balance, ________ are use to _____________. A _________ is written outside the ____________ to indicate the number of polyatomic ions.
ZERO
PARENTHESES are used to enclose the formula of the ion.
a SUBSCRIPT is written outside the CLOSING PARENTHESIS
Ex: the formula for magnesium nitrate (the ions in this compound are the magnesium ion and the nitrate ion, a polyatomic ion)
*see page 139 in text to see the work
44
How do we name ionic compounds containing POLYATOMIC IONS?
It is important that you learn to recognize the _______ ________ in the formula and name it correctly.
As with other ionic compounds, no _______ are used.
When naming ionic compounds containing polyatomic ions, we first write the positive ion, usually a metal, and then we write the name of the polyatomic ion.
It is important that you learn to recognize the polyatomic ion in the formula and name it correctly (see page 140 in text!)
As with other ionic compounds, no prefixes are used.
45
What are the FOUR steps to naming IONIC COMPOUNDS with POLYATOMIC IONS?
1. Identify the CATION and POLYATOMIC ION (ANION)
2. Name the cation using a Roman numeral, if needed.
3. Name the polyatomic ion usually ending with ITE or ATE
4. Write the name of the compound, CATION first and the POLYATOMIC ION second.
46
What is a COVALENT COMPOUND?
Because of the _______ __________ _______ of the nonmetals, electrons are not transferred between atoms but are shared to achieve stability. When atoms share electrons, the bond is called a _______ bond.
When two or more atoms share electrons, they from __________
A COVALENT COMPOUND forms when atoms of two nonmetals share electrons.
HIGH IONIZATION ENERGIES; COVALENT BOND
MOLECULES
47
The simplest COVALENT MOLECULE is _______.
Describe how this molecule is formed.
The result is called a ________ bond, in which the shared electrons give the noble gas arrangement of ______ to each of the ____ atoms.
When the ______ atoms form _____, they are more stable than two individual _____ atoms.
Hydrogen gas (H2)
When two H atoms are far apart, there is no attraction between them. As the H atoms move closer, the positive charge of each nucleus attracts the electron of the other atom. This attraction, which is greater than the repulsion between the valence electrons, pulls the H atoms closer until they share a pair of valence electrons.
The result is called a COVALENT BOND;
He; H
When the H atoms form H2, they are more stable than two individual H atoms.
48
The valence electrons in COVALENT MOLECULES are shown using an _________ __________ (or Lewis structure).
The shared electrons, or _______ ________ are shown as _______ OR _____________.
The nonbonding pair of electrons, or ______ ______ are placed on the _____________.
...using an ELECTRON-DOT FORMULA
The shared electrons, or BONDING PAIRS, are shown as TWO DOTS or A SINGLE LINE BETWEEN ATOMS.
The nonbonding pair of electrons, or LONE PAIRS, are placed on the OUTSIDE.
Ex: a fluorine molecule, F2, consists of two fluorine atoms.
49
__________ (H2) and ________ (F2) are examples on NONMETAL elements who natural state is _________, which means they contain two like atoms.
HYDROGEN; FLUORINE
DIATOMIC, which means they contain two like atoms.
50
The number of electrons that a nonmetal atom shares AND the number of covalent bonds it forms are usually equal to the ___________ to acquire ____________.
...usually equal to the number of electrons it needs to acquire a noble gas arrangement.
Ex: the element carbon combines with hydrogen to form a covalent compound, CH4, methane, which is a component of natural gas.
51
DRAWING ELECTRON-DOT FORMULAS:
| * Draw the electron-dot formula of CH4
We first draw the electron-dot symbols of carbon and hydrogen (see page 142)
Then we can determine the number of valence electrons needed for carbon and hydrogen. When a carbon atom shares its four electrons with 4 hydrogen atoms, carbon obtains an octet and each hydrogen atom is complete with 2 shared electrons.
The electron-dot formula is drawn with the carbon atom as the center atom with the hydrogen atoms on each of the sides.
The bonding pairs of electrons, which are single covalent bonds, may also be shown as simple lines between the carbon atom and each of the hydrogen atoms (see p. 142)
52
What are the exceptions to the OCTET RULE?
* a hydrogen (H2) molecule requires just 2 electrons or a single bond to achieve the stability of the nearest noble gas, helium.
* although the nonmetals typically form octets, atoms such as P, S, Cl, Br, and I can form compounds with 10 or 12 valence electrons. (see page 144)
53
What is a DOUBLE BOND?
What is a TRIPLE BOND?
Atoms of _____, ______, ______ and _____ are most likely to form multiple bonds.
In many covalent compounds, atoms share 2 or 3 pairs of electrons to complete their octets.
A DOUBLE BOND occurs when 2 pairs of electrons are shared.
A TRIPLE BOND occurs when 2 pairs of electrons are shared.
Atoms of carbon, oxygen, nitrogen, and sulfur are most likely to form multiple bonds.
54
DOUBLE and TRIPLE bonds form when _________________________________. Then one or more ________ pairs from the atoms attached to the central atom are shared with the central atom.
...when the number of valence electrons is not enough to complete the octets of all the atoms in the molecule.
LONE PAIRS
55
What are the FOUR steps to drawing ELECTRON-DOT FORMULAS?
1. Determine the arrangement of atoms.
2. Determine the total number of valence electrons.
3. Attach each bonded atom to the central atom with a pair of electrons
4. Place the remaining electrons using simple or multiple bonds to complete octets (2 for H, 6 for B)
56
When naming a COVALENT COMPOUND, the first nonmetal in the formula is named by _______________; the second nonmetal is named __________________, followed by _________.
When a subscript indicates two or more atoms of an element, a ________ is used in front of its name. Why is this needed?
...the first nonmetal in the formula is named by its ELEMENT NAME; the second nonmetal is named USING THE FIRST SYLLABLE OF ITS NAME, followed by IDE.
When a subscript indicates two or more atoms of an element, a PREFIX is used in front of its name.
The names of covalent compounds need prefixes because several different compounds can be formed from the same 2 nonmetals. Ex: carbon and oxygen can form 2 different compounds, carbon monoxide (CO) and carbon dioxide (CO2).
57
When the vowels o and o, or a and o appear together, the first vowel is ____________.
OMITTED, as in carbon monoxide (rather than carbon monooxide)
58
In the name of a COVALENT COMPOUND, the prefix _____ is usually omitted.
Traditionally, however, CO is named _____ ________.
...the prefix MONO is usually omitted, as in NO, nitrogen oxide.
CO is named carbon monoxide, rather than carbon oxide.
59
In the name of a COVALENT COMPOUND, the names of the two nonmetals are given along with ________________.
To obtain a formula, we write ___________.
...given along with prefixes for the number of atoms of each.
To obtain a formula, we write the symbol for each element and a subscript if a prefix indicates two or more atoms.
60
What are the TWO steps to writing formulas for COVALENT COMPOUNDS?
1. Write the symbols in the order of the elements in the name.
2. Write any prefixes as subscripts.
61
This card is a SUMMARY of what you have learned about naming IONIC and COVALENT COMPOUNDS:
1. In general, compounds having 2 elements are named by stating the ___________, followed by the ___________ with an _______ ending.
2. If the first element is a METAL, the compound is usually ________. If the first element is a NONMETAL, the compound is usually ______.
3. For IONIC COMPOUNDS, it is necessary to determine _________________. If so, a ______________ following the name of the metal indicates a particular ionic charge. One exception is _________.
4. IONIC COMPOUNDS having 3 or more elements include some type of ________ _______. They are named by IONIC RULES but have an ___ or ___ ending when the _______ ______ has a negative charge.
5. In naming COVALENT COMPOUNDS having 2 elements, ________ are necessary to indicate two or more atoms of each nonmetal as shown in that particular formula.
1. In general, compounds having 2 elements are named by stating the FIRST ELEMENT NAME, followed by the NAME OF THE SECOND ELEMENT with an IDE ending.
2. Metal- IONIC; nonmetal- COVALENT.
3. ...determine whether the metal can form more than one type of positive ion. If so, a ROMAN NUMERAL following the name of the metal indicates a particular ionic charge. One exception is the AMMONIUM ION (NH4+), which is also written first as a positively charged polyatomic ion.
4. ...include some type of POLYATOMIC ION. They are named by IONIC RULES but have an ATE or ITE ending when the POLYATOMIC ION has a negative charge.
5. PREFIXES
62
What is ELECTRONEGATIVITY?
Which have higher electronegativities: metals or nonmetals? Why?
ELECTRONEGATIVITY is the ability of an atom to attract the shared electrons in a bond.
NONMETALS have higher electronegativities because they have a greater attraction for electrons than metals.
63
On the ELECTRONEGATIVITY SCALE, fluorine was assigned a value of ______, and the electronegativities for all other elements were determined relative to the attraction of fluorine for _________ electrons.
The nonmetals ____ (____) and _______ (____), which are located in the upper right corner of the Periodic Table, have the highest electronegativities.
The metals _______ and _______, which have the lowest electronegativity (_____), are located in the lower left corner of the Periodic Table.
There are no electronegativity values for the _______ ________ because they do not typically form bonds.
4.0; SHARED ELECTRONS
FLUORINE (4.0) and OXYGEN (3.5)
CESIUM and FRANCIUM; 0.7
NOBLE GASES
64
The difference in the ______________ of 2 atoms can be used to predict the type of bond, ionic or covalent, that forms.
ELECTRONEGATIVITY
65
A bond between atoms with identical or very similar electronegativity values is a _______ _________ bond.
NONPOLAR COVALENT BOND
66
When bonds are between atoms with different electronegativity values, the electrons are shared _____________; the bond is a ______ ________ bond.
UNEQUALLY
POLAR COVALENT BOND
67
The _________ of a bond depends on the electronegativity difference.
In a polar covalent bond, the shared electrons are attracted to the more electronegative atom, which makes is partially ______ due to the negatively charged electrons around that atom.
At the other end of the bond, the atom with the lower electronegativity becomes partially _______ due to the lack of the electrons at that atom.
A bond becomes more _________ as the electronegativity difference increases.
POLARITY
NEGATIVE
POSITIVE
POLAR
68
A POLAR COVALENT BOND that has a separation of charges is called a ______. The positive and negative ends of this bond are indicated by the lower-case Greek letter ________ with a positive or negative sign.
Sometimes we use an arrow that points from the ______ charge to the _______ charge to indicate the dipole.
DIPOLE
DELTA
POSITIVE; NEGATIVE
See page 150 for what these look like
69
Variations in bonding are ___________.
When the electronegativity difference is 0.0 to 0.4, the electrons are considered to share _________ in a ________ _________ _______.
As the electronegativity difference ________, the shared electrons are attracted ______ strongly to the more electronegative atom, which __________ the polarity of the bond.
When the electronegativity difference is from 0.5 to 1.8, the bond is a ______ _______ bond.
When the electronegativity difference is greater than 1.8, electrons are transferred from one atom to another, which results in what kind of bond?
Thus, for large differences in electronegativity, we would predict what kind of bond?
CONTINUOUS (there is no definite point at which one type of bond stops and the next starts.
0.0-0.4= the electrons share EQUALLY in a NONPOLAR COVALENT BOND.
As the electronegativity difference INCREASES, the shared electrons are attracted MORE strongly to the more electronegative atom, which INCREASES the polarity of the bond.
POLAR COVALENT BOND
IONIC BOND
We would predict an IONIC BOND
70
Using the information in Section 4.5 about electron-dot formulas, we can predict the ____________ shapes of many ______.
The shape is important in our understanding of _________ interact with enzymes or certain antibiotics or produce our sense of taste and smell.
three-dimensional; molecules
MOLECULES
71
How is the three-dimensional shape of a molecule determined?
...by drawing an electron-dot formula and identifying the number of electron groups around the central atom.
72
What is the VALENCE SHELL ELECTRON-PAIR REPULSION (VSEPR) THEORY?
The electron groups are arranged as far apart as possible around the central atom to minimize the repulsion of the electron groups. The specific shape of a molecule is determined by the number of atoms attached to the central atom.
73
CENTRAL ATOMS WITH 2 ELECTRON GROUPS- two examples:
In BeCl2, two chlorine atoms are bonded to a central beryllium atom. Because an atom of Be has a _______ attraction for valence electrons, it forms a _______ rather than _______ compound. (see p. 153 for electron-dot formula, which is an exception)
In predicting shapes, we count a DOUBLE or TRIPLE bond (2 or 3 electron pairs) as ______ electron group(s).
In the electron-dot formula of CO2, two electrons groups (two double bonds) are on opposite sides of the C atom as far apart as possible, which gives a bond angle of ____ degrees. The shape of the CO2 molecule is ________.
STRONG attraction: COVALENT rather than IONIC compound.
ONE ELECTRON GROUP
180 degrees; LINEAR
See page 153
74
CENTRAL ATOMS WITH 3 ELECTRON GROUPS- two examples:
In the electron-dot formula of BF3, the central atom B has 3 electron groups attached to 3 fluorine atoms (another exception to the octet rule). With the 3 electron groups as far apart as possible, the bond angles are _____ degrees and the shape is _______ _______. In the BF3 molecule, all the atoms are in the same ______ and have bond angles of ______ degrees.
In the electron-dot formula for SO2, there are also 2 electron groups around the sulfur atom: a single-bonded O atom, a double-bonded O atom, and a lone pair of electrons. As in BF3, three electron groups have _____ repulsion by forming a _______ ______ arrangement. However in SO2 one of the electron groups is a one pair. Therefore its shape is determined only the 2 oxygen atoms bonded to the central S atom to give the SO2 molecule a ______ shape.
120 degrees; TRIGONAL PLANAR
...all the atoms are in the same PLANE and have bond angles of 120 degrees.
MINIMAL repulsion by forming a TRIGONAL PLANAR ARRANGEMENT; a BENT shape
see page 153
75
CENTRAL ATOMS WITH 4 ELECTRON GROUPS- three examples:
In a molecule of CH4, the central carbon atom is bonded to 4 electron groups attached to 2 hydrogen atoms. The best arrangement for minimal repulsion is the one with the electron groups at the corners of a ___________ (not planar with 90 degree angles). This gives bond angles of _______ degrees. When there are 4 atoms attached to the 4 electron groups, the shape of the molecule is ___________.
Molecules that have 4 electron groups, but only 2 or 3 attached atoms- like ammonia (NH3). It has 4 electron groups, which have _________ repulsion by forming a ______. However, one of the electron groups is a lone pair. Therefore its shape is determined by only the 3 hydrogen atoms bonded to the central N atom to give the NH3 molecule a _______ _______ shape.
In the electron-dot formula of water (H2O), there are 4 electron groups with have _____ repulsion by forming a _______. However, in H2), two of the electron groups are lone pairs. Therefore its shape is determined by only the 2 hydrogen atoms bonded to the central O atom to give the H2O molecule a ______ shape.
TETRAHEDRON; 109 degrees; TETRAHEDRAL
MINIMAL REPULSION by forming a TETRAHEDRON; a TRIGONAL PYRAMIDAL shape.
MINIMAL REPULSION by forming a TETRAHEDRON; a BENT shape
76
What are the THREE steps for PREDICTING MOLECULAR SHAPE (VSEPR theory)
1. Draw the electron-dot formula.
2. Arrange the electron groups around the central atom to minimize repulsion.
3. Use the atoms bonded to the central atom to determine the molecular shape.
77
MOLECULES with COVALENT BONDS can be ______ or _________, which depends on their bond polarity and their shape.
POLAR or NONPOLAR
78
Molecules such as ____, ____ or ____ are NONPOLAR because ________________.
H2, Cl2, or PH3
...because they contain non polar covalent bonds.
79
Molecules with POLAR bonds can be NONPOLAR if _________________.
Thus a __________ _________ contains nonpolar bonds OR has polar bonds with _______________.
When the polar bonds or dipoles in a molecule cancel each other, the molecule is ________.
...if the polar bonds (DIPOLES) cancel each other in a symmetrical arrangement.
Ex: CO2, a linear molecule, contains 2 polar covalent bonds, whose dipoles point in opposite directions. As a results, the dipoles cancel out, which makes a CO2 molecule nonpolar.
Thus a NONPOLAR MOLECULE contains nonpolar bonds or has polar bonds with dipoles that cancel.
NONPOLAR.
80
In a POLAR MOLECULE, one end of the molecule is more __________ charged than another end.
POLARITY in a molecule occurs when the polar bonds ______________. What three things does this depend on?
NEGATIVELY
DO NOT CANCEL EACH OTHER.
This cancellation depends on the type of atoms, the electron pairs around the central atom, and the shape of the molecule.
81
In POLAR MOLECULES with 3 or more atoms, the __________ determines whether the dipoles cancel or not.
Often there are ______ ________ around the central atom.
In H2O, do the dipoles cancel?
SHAPE OF THE MOLECULE
Often there are LONE PAIRS around the central atom.
In H2O, the dipoles do NOT cancel, which makes the molecule positive at one end and negative at the other end. Thus, water is a POLAR MOLECULE.
82
In GASES, the interactions between particles are ________, which allows gas molecules to move far apart from each other.
In SOLIDS and LIQUIDS, there are sufficient interactions between the particles to ________________, although some solids have low melting points and others have very high melting points.
MINIMAL
HOLD THEM CLOSE TOGETHER
83
_______ properties have high melting points. Explain...
In solids containing molecules with _______ bonds, there are attractive forces, too, but they are weaker than those of an ionic compound.
IONIC
Large amounts of energy are needed to overcome the strong attractive forces between positive and negative ions.
COVALENT bonds
84
What are DIPOLE-DIPOLE ATTRACTIONS?
For polar molecules, attractive forces called DIPOLE-DIPOLE ATTRACTIONS occur between the positive end of one molecule and the negative end of another.
85
What is a HYDROGEN BOND?
When a hydrogen atom is attached to highly electronegative atoms of fluorine, oxygen or nitrogen, there are strong dipole-dipole attractions between the polar molecules. This type of attraction, called a HYDROGEN BOND, occurs between the partially positive hydrogen atom of one molecule and a lone pair of electrons, on a nitrogen, oxygen, or fluorine stop in another molecule.
Hydrogen bonds are the strongest type of attractive forces between polar molecules.
They are a major factor in the formation and structure of biological molecules such as proteins and DNA.
86
Nonpolar compounds do form solids, but at ____ temperatures.
What are DISPERSION FORCES?
Nonpolar compounds do form solids, but at LOW temperatures.
Very weak attractions called DISPERSION FORCES occur between nonpolar molecules. Usually the electrons in a nonpolar molecule are distributed symmetrically. However electrons may accumulate more in one part of the molecule than another, which forms a temporary dipole. Although dispersion forces are very weak, they make it possible for non polar molecules to form liquids and solids.
87
The MELTING POINTS of substances are related to the ________________.
Compounds with ______ attractive forces such as dispersion forces have _______ melting points because a _______ amount of energy is needed to separate the molecules and form a liquid.
Compounds with hydrogen bonds and dipole-dipole attractions require ________ energy to break the attractive forces between the molecules.
The highest melting points are seen with _____ compounds that have _________ attractions between ions.
Strength of the attractive forces.
WEAK; LOW; SMALL
MORE
IONIC; VERY STRONG
see page 155 (and TABLE 4.16 showing the molecular shapes for a central atom with 2, 3 and 4 bonded atoms!)
