Chemical Bonding Flashcards
Compound
is a substance that is made up of two or more different elements combined together chemically.
Octet Rule
that when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell.
An Ion
is a charged atom or group of atoms.
An Ionic Bond
is the force of attraction between oppositely charged ions in a compound.
A transition metal
is one that forms at least one ion with a partially filled d sublevel.
Molecule
is a group of atoms joined together. It is the smallest particle of an element or compound that can exist independently
What is the smallest particle of an element or compound that can exist independently?
Molecule
What is the valency of an element defined as?
Valency of an element is defined as the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines.
Electronegativity
is a measure of the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond.
What does a difference > 1.7 in electronegativity indicate?
difference > 1.7 indicates ionic bonding in a compound
What does a difference lower or equal to 1.7 in electronegativity indicate?
An electronegativity difference lower or equal to 1.7 indicates covalent bonding in a compound.
What happens to the value of electronegativity down the groups in the Periodic Table?
decrease down the groups in the Periodic Table for two reasons: increasing atomic radius and screening effect of inner electrons
What happens to the value of electronegativity across the periods in the Periodic Table?
The values of electronegativity increase across the periods in the Periodic Table for two reasons: increasing nuclear charge and decreasing atomic radius.
What is the most electronegative element?
F = most electronegative element (flourine)
What happens as you go down the group of halogens and why?
Halogens - decrease in reducing power down the group due to drop in electronegative values.
Compound
A compound is a substance that is made up of two or more different elements chemically combined. Element+Element=Compound
What are atoms held together by?
Chemical bonds
What is special about noble gases?
Noble gases have 8 electrons on their outer shell and are quite stable. Generally unreactive.
Are noble gases reactive?
Generally unreactive
What is helium used in and why?
Airships as it is lighter than air
How heavy is helium compared to hydrogen and why is it especially good to be used in airships?
Not as light as hydrogen [twice as heavy per volume] but does not burn
What does helium do to the voice and why?
It gives the diver a “Mickey Mouse” voice because it has such a low density compared to air
What is the most common Noble Gas?
argon
What is argon used for?
Used to fill normal light bulbs to stop them imploding
What happens when bonding occurs?
When bonding occurs, atoms tend to reach an electron arrangement with 8 electrons in the outer shell
What are the limitations of the octet rule?
Hydrogen, Lithium, Transition elements
What is valency?
Valency is the number of bonds an atom makes when it reacts.
How can the valency be worked out?
By calculating the number of electrons an atom needs to lose/gain to have 8e- on it’s outer shell.
How can valency be predicted?
From the periodic table
What does ammonia contain and what is it’s chemical formula?
Ammonia contains only Nitrogen and Hydrogen. It’s chemical formula is NH3.
What does methane contain? What is it’s chemical formula?
Methane contains only carbon and hydrogen. It’s chemical formula is CH4.
What is the chemical formula of Calcium Bromide?
CaBr2
What is the chemical formula of Silicon Flouride?
SiF4
What is a transition metal?
A transition metal is one that forms at least one ion with a partially filled d sublevel
What are features of transition elements?
Transition elements have variable valency, form coloured compounds and are used as catalysts.
What are exceptions to transition elements?
Exceptions: Zinc (Zn) and Scandium (Sc)
What is an ion?
a charged atom or group of atoms
What is involved in Ionic Bonding?
Electrons are transferred and ions are formed
are cations positive or negative?
positive
are anions positive or negative?
negative
What is an ionic bond?
the force of attraction between oppositely charged ions in a compound
What is ionic bonding usually between?
Ionic bonding usually between Groups 1 and 2 (Metals) and Groups VI and VII (Non-metals)
Draw dot and cross diagrams
.
What structure do ionic substances usually form and give an example.
Ionic substances usually form a structure called a crystal lattice e.g. NaCl
Why do ionic substances form crystals?
Ionic substances form crystals because positive ions attract negative ions in all directions
What are the characteristics of ionic substances?
Strong forces between the ions means it is very hard to break up the lattice structure.
Cannot conduct electricity when solid.
Most dissolve in water.
When dissolved the ions can conduct electricity
What is the result of ionic substances having strong forces between ions?
- High melting points and boiling points
- Usually solid at room temperature
Why are ionic substances not able to conduct electricity when solid?
- Ions not free to move and carry electricity
What are examples of everyday ionic substances?
Table Salt - Sodium Chloride (NaCl)
Flouridation in water to prevent tooth decay
- Sodium Fluoride (NaF)
What are the main complex ions with one negative change and their formulae?
Hydroxide ion (OH-), Nitrate ion (NO3-), Hydrogencarbonate ion (HCO3-), Permanganate ion (MnO4-)
What are the main complex ions with two negative charges and their formulae?
Carbonate ion (CO3 2-), Chromate ion (CrO4 2-), Dichromate ion (Cr2O7 2-), Sulfate ion (SO4 2-), Sulfite ion (SO3 2-), Thiosulfate ion (S2O3 2-)
What are the main complex ions with three negative charges and their formulae?
Phosphate ion (PO4 3-)
What are the main complex ions with one positive charge and their formulae?
Ammonium ion (NH3+)
Covalent bond
Formed when atoms share electrons
Give examples of covalent bonds
H2 - Hydrogen molecule
Cl2 - Chlorine molecule
What is a single bond and give an example
1 pair of electrons shared - H2
What is a double bond and give an example
2 pairs of electrons shared - O2
What is a triple bond and give an example
3 pairs of electrons shared - N2
Draw dot and cross diagrams for H2, O2 and N2
.
What are bonding pairs?
Shared electron pairs that form covalent bonds
What are lone pairs?
Electron pairs not involved in bonding
What happens to orbitals in a convalent bond?
they overlap
What is a sigma bond formed by?
Formed by the head-on overlap of two orbitals (can be s-orbitals or p-orbitals)
What is a pi-bond formed by?
Formed by the sideways overlap of p-orbitals
What type of bond is stronger and why?
Sigma bonds are stronger than pi bonds as there is more overlap between orbitals
How many sigma bonds and pi bonds in a double bond?
One sigma and one pi
How many sigma bonds and pi bonds in a triple bond?
One sigma and two pi
What are the features of ionic bonding?
Transfer of electrons, ions formed, high melting and boiling points, usually solid at room temp., conduct electricity when dissolved in water or molten (the ions are free to move in these stated)
What are the features of covalent bonding?
Sharing electrons, covalent bonds formed, usually low melting and boiling points, usually liquid or gaseous at room temperature, do not conduct electricity (no ions present)
Which is stronger, sigma or pi bonding?
sigma
Which has more overlap, sigma or pi bonding?
sigma
Which can only happen with p orbitals, sigma or pi bonding?
Pi
Which can happen with both s and p orbitals, sigma or pi bonding?
Sigma
Which has a head on overlap, sigma or pi bonds?
sigma
Which has a sideways overlap, sigma or pi bonds?
pi
What shape are s and p orbitals?
s = spherical, p = dumb bell
How many sigma bonds and pi bonds in a single bond?
1 sigma
What are intermolecular forces?
Attraction (replusive) forces between molecules
What are intramolecular forces?
attractive (repulsive) forces within a molecule
What are Van der Waals Forces?
are weak attractive forces between molecules resulting from the formation of temporary dipoles
What is a dipole-dipole?
Dipole-dipole forces are forces of attraction between the negative pole of one molecule and the positive pole of another.
What are hydrogen bonds?
are particular types of dipole-dipole attraction between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or flourine.
What is the Law of the Conservation of Mass?
The total mass of the products of a chemical reaction is the same as the total mass of the reactants.
What is the Law of the Conservation of Matter?
That in any chemical reaction, matter is neither created nor destroyed but merely changes from one form into another.
Draw a linear molecule shape?
180 degrees
Draw a v-shaped or bent molecule shape?
104.50 degrees
Draw a trigonal planar molecule shape?
120 degrees
Draw a tetrahedral molecule shape?
109.5 degrees
Draw a trigonal pyramidal molecule shape?
107 degrees
What do electrons in bonding pairs do?
electrons in the bonding pairs repel each other and want to be as far apart as possible
What are the no. of electron pairs, no. of lone pairs, bond angle and shape of molecule NH3?
No. of electron pairs = 4
No. of lone pairs = 1
Bond angle = 107 degrees
Shape of molecule = Pyramidal
What are the no. of electron pairs, no. of lone pairs, bond angle and shape of molecule H2O?
No. of electron pairs = 4
No. of lone pairs = 2
Bond angle = 104.5 degrees
Shape of molecule = V-shaped
When are molecules formed?
When atoms are joined together by covalent bonds
What dictates the shape of the molecule?
The arrangement of the atoms
How do you figure of the arrangement of atoms in a molecule?
The Electron Pair Repulsion Theory
Where are lone pairs of electrons? What does this cause?
They are closer to the nucleus of the atom (nuclear charge sucks them in). Because of this they are closer together (create a strong negative charge)
What does the collective nuclear charge of lone pairs of electrons do?
Pushes the bonding pairs further apart, decreases the bond angle and distorts the shape of the molecule
What are examples of molecules with lone pairs of electrons?
Water - H2O
Ammonia - NH3
What do atoms in covalent bonds do?
share electrons
When the atoms in a covalent bond share the electrons equally, what is the bond said to be? What are examples of this?
non-polar
E.g. H2, N2, O2
When the atoms in a covalent bond share the electrons unequally, what is the bond said to be? What are examples of this?
Polar
E.g. HCl, NH4
How do we figure out whether a bond is polar or non-polar?
We figure it out by looking at the electronegativity
What is electronegativity?
Electronegativity is the relative attraction an atom has for a shared pair of electrons in a single covalent bond.
What does greater electronegativity cause?
greater pull on the electrons
How do you work out the electronegativity?
The electronegativity table pg 81 of log tables
What happens to the atoms with the greater pull on the electrons in the bond? What happens to the other atom? Give examples and examples of how it is seen.
The atom with the greater pull on the electrons becomes slightly negative while the other atom in the bond becomes slightly positive. E.g. H2O, HCl, KBr, Kl, LiBr. 1. Charged rod 2. “Like dissolves in like”
What can electronegativity be used to predict?
the nature of a bond
What are the natures of bonds
Bonds = Ionic and Covalent Covalent = Polar bonds and Non-polar bonds
What are polar bonds in everyday life?
Water (good solvent for ionic and polar substances)
Ethanol (used in alcoholic beverages)
What are non-polar bonds in everyday life?
Tetrachloroethene (used in dry cleaning)
Propanone (also called acetone) (used in nail varnish remover)
Can a molecule that has polar bonds be non-polar overall?
A molecule that has polar bonds can be non-polar overall if it is one of the following shapes:
- Linear
- Trigonal planar
- Tetrahedral
(i. e. shapes with no lone pairs)
Give examples of molecules that have polar bonds but are non-polar overall?
e.g. BeH2, BF3, CH4
When can a molecule that has polar bonds be non-polar overall? Do they have lone pairs?
A molecule that has polar bonds can be non-polar overall if it is one of the following shapes:
- Linear
- Trigonal planar
- Tetrahedral
(i. e. shapes with no lone pairs)
If a molecule is not symmetrical what shapes is it? Does it have a lone pair? Give examples.
If the molecule is not symmetrical it is one of the following shapes: (has lone pair)
Pyramidal
V-shaped
e.g. NH3, H2O
Do molecules with polar bonds have to be polar molecules? Why?
Some molecules even though they have polar bonds doesn’t mean they are polar molecules due to their shapes (shape is symmetrical as there are no lone pairs of electrons)
Draw a diagram of non-polar molecule CO2?
.
Draw a diagram of polar molecule H2O?
.
Draw a diagram of polar molecule NH3?
.
Give examples of molecules with polar bonds which are not polar molecules?
e.g. Carbon dioxide, Chloroform, boron trichloride.
What is intramolecular? give an example
within the molecule e.g. between an oxygen atom and a hydrogen atom in a molecule
What is intermolecular? give an example
between molecules e.g. between water molecules
How many types of inter molecular bonding are there? What are they called?
- Van der Waals 2. Dipole-dipole 3. Hydrogen
What are Van der Waal forces?
Van der Waal forces are weak forces of attraction between temporary dipoles
Can temporary dipoles be set up in non-polar molecules?
Temporary dipoles can be set up in non-polar molecules e.g. H2
Can forces of attraction be set up between oppositely charged poles in the atom
Weak forces of attraction can be set up between oppositely charged poles in the atom
What are features of temporary dipoles?
Do not last very long
Weakest of the three
Low boiling points
What are dipole-dipole forces?
Dipole-dipole forces are forces of attraction between the negative pole of one molecule and the positive pole of another
What poles do polar molecules have? Give an example
Polar molecules have positive and negative poles e.g. HCl.
What can happen to the positive pole of one polar molecule?
The positive pole of one molecule can become attracted to the negative pole of another
What is the main feature of polar molecules?
Much weaker than ionic bonds
What is hydrogen bonding?
Hydrogen bonding occurs in molecules where a hydrogen atom is bonded to Nitrogen, Oxygen or Flourine. The hydrogen carries a positive charge and is attracted to the electronegative atom in another molecule.
What are the features of hydrogen bonding?
Strongest of the three
N, O and F are very electronegative (when bonded with hydrogen, the electron spends more time on the N, O or F creates strong poles
High boiling points
Mole
The amount of a substance which contains 6 X 10 to the power of 23 particles of that substance
(avogadro’s number or constant = L)
How do you find Kelvin?
Celsius +273
What is 0 degrees celsius/standard temperature in Kelvin?
273 K
What is room temp./normal temp. in Kelvin?
293 K
What is standard pressure?
1X10 to the power of 5 Pa (100kPa) (small k = kilo)
What is 1 litre in cm squared?
1000 cm squared
What does Boyle’s Law state?*
*Irish - Robert Boyle
At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure
What does Charles’ Law state?
At constant pressure, the volume of a fixed mass of a gas is directly proportional to its temperature measured on the Kelvin scale
What is the General Gas Law?
P1 X V1 over T1 = P2 X V2 over T2
Temp. in Kelvin, Units for Volume same each side, Units for pressure same each side
What is Gay Lussac’s law of Combining Volumes?
The volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided the volumes are measured at the same temp. and pressure
What does Avogadro’s Law state?
That equal volumes of gases contain equal numbers of molecules under the same conditions of temp. and pressure
What is molar volume?
At s.t.p (standard temperature and pressure) one mole of any gas occupies 22.4 litres
Remember to watch out for r.t.p in questions
room temp. and pressure = as given in Q (often 24 litres)
What is ideal gas?
One which perfectly obeys all the gas laws and all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure.
How many scales of temperature in science?
celsius and kelvin
What is the pressure of a gas?
The pressure of a gas is the force that the gas exerts on each unit area (e.g. one square meter) of its container
What is the SI unit for pressure?
Newtons per meter squared (N/m squared)
Also called the pascal (Pa)
What is normal atmospheric pressure?
1x10 to the power of 5 N/m squared
1x10 to the power of 5 Pa
What is used in pascals when numbers are very large?
kilopascals
What does volume mean?
How much space something takes up
What will a gas fill?
all available space
What is the volume of a sample of gas the same as?
The volume of a sample of gas is the same as the container that it is held in.
What is the SI unit for volume?
cubic meter (m to the power of 3)
other than the SI unit of cubic meter what units are used to express volume?
centimetres cubed
Litre (also known as dm to the power of 3)
As the pressure goes up what happens to the volume?
It goes down
What is Boyle’s Law?
At constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure
What happens as the temperature (K) goes up? What is the limitation of this?
so does the pressure - only works when temperature is on Kelvin scale
What is it assumed gases are made up of in The Kinetic Theory of Gases?
Gases are made up of particles that are in continuous rapid, random motion, colliding with each other and with the walls of the container.
What is it assumed about forces in between the particles of a gas in The Kinetic Theory of Gases?
There are no attractive or repulsive forces between the particles of a gas.
What is assumed about the volume of all particles compared to the space they occupy in The Kinetic Theory of Gases?
The gas particles are so small and so widely separated that the total volume of all particles are so widely separated that the total volume of all particles is negligible compared with the space that they occupy
What is assumed about collisions between particles in The Kinetic Theory of Gases?
Collisions between particles are perfectly elastic, i.e. there is no overall loss of kinetic energy in these collisions
What is assumed about the average kinetic energy of the particles in a gas in The Kinetic Theory of Gases?
The average kinetic energy of the particles in a sample of a gas is proportional to the temperature measured on the Kelvin scale.
What are the limitations regarding the Kinetic Theory of Gases referring to the forces of attraction between the particles of a gas?
Contrary to assumption 2, there are forces of attraction between the particles of a gas, e.g. van der Waals forces/ Dipole-dipole forces
What are the limitations regarding the Kinetic Theory of Gases referring to total volume of gas compared to the space it occupies?
Contrary to assumption 3, it is not valid to say that the total volume of gas is always negligible compared with the space that they occupy.
What is the result of the two assumptions in the Kinetic Theory of Gases being not strictly true?
Since the two assumptions are not strictly true, the kinetic theory of gases can only apply perfectly to what might be termed an ideal gas - no such gas exists
What is an ideal gas?
An ideal gas is one that perfectly obeys all the assumption of the kinetic theory of gases under all conditions of temperature and pressure
When do cases deviate most from ideal behavior? (Referring to The Kinetic Theory of Gases)
Cases deviate most from ideal behaviour when:
Under high pressure (the particles are forced close together)
At low temperature (particles moving slowly)
Under the conditions in which cases tend to deviate most from ideal behaviour, what changes about forces and volume (Referring to The Kinetic Theory of Gases)
Under these conditions, the effect of intermolecular forces becomes significant and the volume of the particles cannot be ignored when compared to the volume in which they move
When do gases come closest to ideal behaviour?(Referring to The Kinetic Theory of Gases)
Gases come closest to ideal behaviour when particles are separated from each other:
Low pressure
Higher temperatures
What do the majority of gases under normal conditions conform to? What is this more the case with?
(Referring to The Kinetic Theory of Gases)
Majority of gases (under normal conditions) conform reasonably well to ideal behaviour. More the case with non-polar particles because van der Waals forces are relatively weak
