CHEM Unit 5 - Chemical Bonding

Bonds

forces that hold groups of atoms together and makes them function as a unit

Ionic Bonds

gain or lose electrons with other atoms

electrons are transferred between metals and nonmetals

Atom Activity in Ionic Bonds

metals form cations +

nonmetals form anions -

Lewis Dot Structure

shows the valence e- of atom through dots

an arrow is used to show the transfer of electrons from metal to nonmetal

Properties of Ionic Compounds

bonds are strong - high melting point

compounds are solid at room temp

conduct electricity in the aqueous state when it is dissolved in water

Ionic Compounds Form

crystals - a 3d repeating pattern of positive and negative ions

Covalent Bonds

bonding by sharing electrons to achieve a full outer shell/noble gas config

formed between 2 nonmetals

Covalent Bond Symbol

circle shows sharing of electrons

Molecule

a neutral group of 2 or more atoms held together by a covalent bond

Diatomic Molecules

gases that do not exist in nature as single atoms, they bond together to form a molecule

composed only of atoms of the same type

always subscript of 2

Diatomic Molecule List

HOBrFINCl

Molecular Formula

ex. CH4

Structural Formula

shows the arrangement of atoms and the covalent bonds between them

Single Bond

a single covalent bond is made up of 2 electrons

Paired Electrons

a pair of electrons on 1 side of the chemical symbol in electron dot structure

Unpaired Electron

a single electron on 1 side of the chemical symbol in electron dot structure

Shared Electrons

a pair of electrons between 2 atoms involved in a bond

Unshared Electrons

a pair of electrons not involved in a bond, can be found on the central atom as well as the bonding atoms

How to Determine Central Atom in a Molecule

When 2+ atoms, the atom that wants to make the most bonds is the central atom

Properties of Covalent Compounds

much lower melting and boiling points

gases and liquids at room temp

does not conduct electricity in water

soft and squishy

Electron Deficient

compounds in which an element has a incomplete octet

Expanded Octet

compounds in which an element contains more than 8 electrons

VESPR

Valence Shell Electron Pair Repulsion

VESPR Theory

This theory states that the repulsion between electron pairs causes molecules to adjust their shape so the valence electron pairs stay as far apart as possible

5 basic shapes

linear, bent, pyramidal, trigonal planar, tetrahedral

VESPR In Action

it is the unshared pairs on the central atom that force attaching atoms in a downwards position

Molecular Shapes with Central Atom Unshared Electrons

Linear, no
linear(3), no

bent, yes

pyramidal, yes

trigonal, no

tetrahedral, no

AXE Model

A - central atom
X - # of bonding atoms

E - # of electron pairs

Electronegativity

the ability of an element to attract electrons

Why are valence electrons important?

determine charge + bonding

Nickname for Covalent Bond

molecular bond

Polarity Determination

a molecule can be polar or nonpolar depending on the electronegativity difference between atoms that share electrons

Polar Covalent Bond

a bond where atoms are shared unequally

ex. HF

Non Polar Covalent Bond

a bond where electrons are shared equally
ex, F2

Electronegativity Difference

<0.4, nonpolar

>=0.4, polar

Polarity Important Note

Polarity only exists for covalent bonds

if there is a metal(ionic bond), can’t find

Does the presence of one or more polar bonds aways result in a polar molecule?

no

Polar Molecule Characteristics

polar bonds and asymmetrical shape

Asymmetrical Shapes

bent and pyramidal

Symmetrical Shapes

same linear, trigonal planar, and tetrahedral

Non Polar Molecule Characteristics

all bonds are non polar

1+ bonds are polar and molecule is symmetrical

Polyatomic Ion Electron Rules

add total ve

add 1 ve for each negative charge and subtract 1 ve for each positive charge

place 2 electrons between each pair of atoms then distribute remaining electrons by giving preference to most electronegative atoms first

put brackets