2. Chemical Bonding

i was going to make a joke about sodium and hydrogen, but NaH!

compound

a substance that is made up of two or more different elements chemically combined

octet rule

atoms tend to undergo chemical changes in order to reach an electron arrangement with eight electrons in their valence shell

compound

a substance that is made up of two or more different elements chemically combined

octet rule

atoms tend to undergo chemical changes in order to reach an electron arrangement with eight electrons in their valence shell

valency

the number of bonds an atom of that element forms when it reacts

valence electrons

the number of electrons in the outer energy level of an atom of an element

to write chemical formula using valency

write down valency of each element, work out ratio needed, write formula

ionic bond

the force of attraction between oppositely charged ions in a compound

ionic bonding generally occurs between…

metals and non-metals

ionic compounds are held together in a…

crystal lattice structure

NaCl structure

each sodium ion (+) is surrounded by 6 chloride ions (-), each chloride ion is surrounded by 6 sodium ions

ionic electronegativity difference

1.7+

hydroxide ion

OH⁻

nitrate ion

NO₃⁻

permanganate ion

MnO₄⁻

hydrogencarbonate ion

HCO₃⁻

carbonate ion

CO₃²⁻

sulfate ion

SO₄²⁻

sulfite ion

SO₃²⁻

thiosulfate ion

S₂O₃²⁻

phosphate ion

PO₄³⁻

ammonium ion

NH₄⁺

transition metal

one that forms at least one ion with a partially filled d sublevel

transition metals show…

variable valency

what does (II) mean in iron (II) carbonate?

valency of 2

ionic substances characteristics

strong force of attraction between ions, high melting point, hard solids at room temperature, only conducts electricity when molten or dissolved

everyday ionic substances

salt tablets - taken to replce lost salt from sweating, brine - solution of sodium chloride used as a preservation process

covalent bonding involves…

sharing of electrons between atoms

single covalent bond

when a pair of electrons is shared between two atoms

double covalent bond

when two pairs of electrons are shared between two atoms

triple covalent bond

when three pairs of electron are shared between two atoms

covalent electronegativity difference

0-0.4-1.7

covalent compounds characteristics

contain individual molecules, liquids, gases, or soft solids at room temp, does not conduct electricity, low melting and boiling points

VSEPR theory

valence shell electron pair repulsion

VSEPR theory is based on…

the idea that electron pairs in valence shells repel each other

shape of molecule depends on…

number of electron pairs around the central atoms

types of molecule shapes

linear, triangular planar, tetrahedral, pyramidal, v-shaped

linear molecule

2 bond pairs, 180° angle, BeH2

triangular planar molecule

3 bond pairs, 120° angle, BeCl3

tetrahedral molecule

4 bond pairs, 109.5° angle, CH4

pyramidal molecule

3 bond pairs, 1 lone pair, 107° angle, NH3

v-shaped molecule

2 bond pairs, 2 lone pairs, 104.5° angle, H2O

to determine shape of molecule

count valence e- of central atom, add one e- for each bonding atom, divide total by 2 to get electron pairs, identify types of electron pairs and predict shape

lone pairs have…

extra repulsion power

why is the angle between v-shaped smaller than pyramidal?

v-shaped has more lone pairs, lone pairs have extra repulsion power

electronegativity

the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond

to find electronegativity difference

take away bigger number from smaller number of elements in a compound and refer to pauling scale

pauling scale

0--[non-polar covalent bond]--0.4--[polar covalent bond]--1.7--[ionic bond]-->

non-polar covalent bond

a bond in which there is equal sharing of the two electrons in the bond

polar covalent bond

a bond in which there is unequal sharing of the pair (or pairs) of electrons

intramolecular bonds

bonds within a molecule, holding the molecule together

polar vs non-polar MOLECULES

polar - centers of partial positive and partial negative do NOT coincide, non-polar - centers of partial positive and partial negative DO coincide

polar or non-polar liquid?

polar liquid - stream of liquid bends towards negatively charged rod (attraction), non-polar liquid - stream of liquid doesn't bend (no attraction)

polar liquid example

water

non-polar liquid example

cyclohexane

intermolecular forces

the forces of attraction that exist between molecules

van-der-waals forces

weak, temporary forces of attraction between neighbouring molecules as a result of temporary dipoles

dipole-dipole forces

forces of attraction between the negative pole of one polar molecule and the positive pole of another polar molecule

hydrogen bonds

a specific type of permanent dipole-dipole attraction between a hydrogen atom of one molecule and a small, highly electronegative atom (N/O/F) of a neighbouring molecule

compound boiling points (highest to lowest)

ionic bonds, hydrogen bonding, dipole-dipole, van der waals

solubility of compounds

like dissolves like

to test solubility

put a few cm3 of water into a test tube, place spatula tip of solid substances/cm3 of one of the liquids into the test tube, put a stopper in and shake, note whether the substance has dissolved or not