4. Chemical Bonds Flashcards
Gilbert Lewis (1916)
-lack of chemical reactivity of noble gases indicates a high degree of stability of their electron configuration (filled valence shell)
Octet rule
-When undergoing chemical reactions, atoms of Group 1A-7A tend to gain, lose or share sufficient electrons to achieve eight valence electrons
Anion
-atoms with almost eight valence electron
-tend to gain electrons ➡️ negatively charged ion
Cation
-atoms with only one or two valence electron
-tend to lose electron ➡️ positively charged ion
Reasons why octet rule is not perfect
- Ions of period 1 and 2 elements with charges greater than +2 are unstable. (i.e., unstable ang B+3, C+/-4)
- Does not apply to Group 1B-7B (transition elements). (i.e. Cu can either be Cu+1 or Cu+2)
Atoms and their ions are…
completely different chemical species and have completely different chemical and physical properties
(i.e. sodium and chlorine atoms are both poisonous. However, NaCl (sodium and chlorine ions) is a common table salt)
(i.e. F2 poisonous and corrosive gas. F- ion in the form of NaF is used for toothpastes)
Naming monoatomic ions
•Elements of Group 1A, 2A, 3A form only one type of cation
-name of metal followed by “ion”
-i.e. Na+ sodium ion
•Transition elements form more than one type of cation
-write the charge in roman numeral right after the name of metal (i.e. Cu+2 Copper (II) ion)
-no need to do this if the transition element can only form one cation (i.e. Ag+ Silver ion)
Naming monoatomic anions
-adding -ide to the stem part of the name
-i.e. F- Fluoride, O2-, Oxide
TWO MAJOR TYPES OF CHEMICAL BONDS
1. Ionic bond
-Chemical bond resulting from the attraction between a cation and anion (lose/ gain electrons)
-usually formed between metal and nonmetal
TWO MAJOR TYPES OF CHEMICAL BONDS
2. Covalent Bond
-bond resulting from sharing of electrons between two electrons
-two nonmetals or nonmetal and metalloid
Electronegativity
-measure of an atom’s attraction for the electrons it shares in a chemical bond
Linus Pauling (1930s)
-Pauling scale: most widely used scale of electronegativity
-Fluorine (most electronegative element), with a value of 4.0
-other elements are assigned values relative to fluorine
Electronegativity and ionization energy
•Ionization energy- amount of energy necessary to remove electron from an atom
•Electronegativity- how tightly an atom holds the electrons that it shares with another atom
-same trend sila; increases left to righr, bottom to top
Forming ionic bonds
-transfer of one or more valence electrons from an atom of lower electronegativity to the valence shell of an atom of higher electronegativity
-difference of electronegativity is 1.9 or greater
Predicting formulas of ionic compound
-the total number of positive charges must equal the total number of negative charges (i.e. Al+3 and S-2 ➡️ Al2S3)
-subscripts in the formulas for ionic compound represent the ratio of ions; reduce to lowest term (i.e. BaO)
How to name ionic compounds
1. Binary ionic compounds of metals that form only one positive ion
-name of the metal from which the cation was formed, followed by the name of anion (i.e. AlCl3 aluminum chloride)
How to name ionic compounds
2. Binary ionic compound of metals that form more than one positive ion
-use roman numerals in the name to show charge
-for common names, use the -ous/ -ic system
-i.e. Copper (II) oxide or cupric oxide
Copper (I) oxide or cuprous oxide
How to name ionic compounds
3. Ionic compounds that contain polyatomic ions
-name the positive ion first and then the negative ion, separate word
-i.e. (NH4)2SO3 ammonium sulfite
NaH2PO4 sodium dihydrogen phosphate
Formation of covalent bond
-electron pairs are shared between two atoms
-filld the valence shell of each electron
-electronegativity difference is less than 1.9
Nonpolar covalent bond
-electrons are shared equally
-difference of electronegativity: Less than 0.5
Polar covalent bond
-electrons are shared unequally
-electronegativity difference 0.5-1.9
-more electronegative atom gains greater fraction of shared electrons; gains partial negative charge
-less electronegative atom gains lesser fraction of shared electrons; gains partial positive charge
Dipole
-chemical species which there is a separation of charge; positive and negative poles
Bonding electrons
Valence electrons involved in forming a covalent bond (shared electrons)
Nonbonding electrons
Valence electrons not involved in forming covalent bonds (unshared electrons)
Single bond
A bond formed by sharing one pair of electrons and represented by single line between two atoms
Lewis structure
A formula for a molecule or ion showing all pairs of bonding electron as single/ double/ triple bonds and all nonbonded electrons as pair of lewis dots
Structural formula
-Formula showing how atoms in a molecule or ion are bonded together
-similar to lewis structure BUT shows ONLY THE BONDING PAIRS of electrons
Double bond
-sharing of two pairs of electrons represented by two lines
-most common between atoms of C, N, O, S
Triple bond
-sharing of three pairs of electrons represented by three lines
-most common between atoms of C and N
Exceptions to octet rule
-molecules that contain an atom with more than eight electrons in its valence shell
-atoms of period 3 elements have one 3s, three 3p, and five 3d orbitals; can accommodate more than eight electrons in their valence shell
-i.e. phosphine (8 electrons at P)
Phosphorus pentachloride (10 e)
Phosphoric acid (10 e)
How to name binary covalent compound
- Name the less electronegative element
- Name the more electronegative element and add -ide
- Use prefixes di-, tri-, tetra- etc. Omit mono when it refers to the first atom named, and it is rarely used with second atom (except carbon monoxide)
-i.e. N2O Dinitrogen oxide
Trivia
Dinitrogen oxide aka?
Nitrous oxide
Laughing gas
Hahahahahaha
Resonance
-A theory that many molecules and ions are best described as hybrid of two or more Lewis contributing structures
-Linus Pauling (1930s)
Contributing structure/ resonance structure/ resonance contributors
-representations of a molecule or ion that differ only in the distribution of valence electron (ibat ibang version ng lewis structure ng molecule)
Resonance hybrid
-molecule or ion described as a composite or hybrid of a number of contributing structures
-interconnecting various contributing structures with double headed arrows
Writing acceptable contributing structures
- All contributing structures must have the same number of valence electrons
- All contributing structures must obey the rules of covalent bonding.
-max 2 electrons for hydrogen
-max 8 electrons for period 2 elements
-max 12 for period 3 elements (i.e. P,S) - The positions of all nuclei must be the same in all structures (DIFFER ONLY IN VALENCE ELECTRONS DISTRIBUTION)
- All structures must have the same number of paired and unpaired electrons
How to predict bond angles in covalent molecules
-using Valence-Shell Electron-Pair Repulsion (VSEPR) model
Bond angle
The angle between two atoms bonded to a central atom
Valence-Shell Electron-Pair Repulsion (VSEPR) model
-like charges repel so the various region of electron density around an atom (bonded and unshared electrons) spread out so that each is as far away as possible from the others
Common Predicted Molecular Shapes (VSEPR model)
1. Linear
•Regions of density around central atom: 2
•Predicted bond angle: 180°
•Examples: CO2, Acetylene (C2H2)
Common Predicted Molecular Shapes (VSEPR model)
2. Trigonal planar
•Regions of density around central atom: 3
•Predicted bond angle: 120°
•Examples: Ethylene (C2H4), Formaldehyde (CH2O)
Common Predicted Molecular Shapes (VSEPR model)
3. Tetrahedral
•Regions of density around central atom: 4
•Predicted bond angle: 109.5°
•Examples: CH4, NH3, H2O
How to determine if a molecule is polar
- It has polar bonds
- Its centers of partial positive charge and partial negative charge lie at different places within molecule
