Chemistry Definitions

Atom

An atom is the smallest particle of matter and is made up of protons, neutrons and electrons

Element

Element is only made up of one sort of atom. They are all listed in the periodic table

Molecule

Molecule is two or more atoms covalently bonded together. The bonding can be either ionic or covalent

Compound

Compound has two or more different types of atom bonded together. The bonding can be either ionic or covalent

Mixture

Mixture has two or more different elements and/or compounds in the same space and can be separated into the individual components.

Acid

An acid is a substance that donates H+ ions

Base

A base is a substance that accepts H+ ions

Alkali

An alkali is a base that releases hydroxide ions in aqueous solution

Salt

A salt is formed when the hydrogen ions from an acid are replaced by a metal or ammonium ion

Atomic number

The number of protons in the nucleus of an atom

Mass number

The number of protons and neutrons in the nucleus of an atom

Isotopes

Atoms of the same element with a different number of neutrons

Why do Isotopes have the same chemical properties?

They have the same electron configuration

Isotopic mass

The mass of an isotope relative to 1/12th the mass of an atom of carbon 12

Relative atomic mass

The weighted average mass of all the isotopes relative to 1/12th the mass of an atom of carbon 12

Isotopic peaks

Some molecules will contain 13C or 2H

Outlier Elements

Cr and Cu are more stable with half full and full 3d sub shells respectively

Ionisation energy

The energy needed to remove one mole of electrons from one mol of atoms in the gaseous state

Relative atomic mass

The weighted average mass of all the isotopes relative to 1/12th the mass of an atom of carbon 12

Relative formula mass

The mass of one formula unit of an ionic compound relative to 1/12th the mass of an atom of carbon 12

The mole

The amount of substance that contains as many particles as there are in exactly 12 grams of carbon 12

Empirical formula

The simplest whole number ratio of atoms of each element present in a molecule

Molecular formula

The actual number of atoms of each element present in a molecule

Ionic Bond

The electrostatic attraction between oppositely charged ions

Metallic Bond

The attraction between positive ions and delocalised electrons

What is the charge on CN

negative one

what is the charge on HPO4

negative 2

what is the charge on SO3 and SO4

negative 2

Coordinate/dative covalent

A covalent bond which both electrons of the shared pair come from the same atom

How is a coordinate bond formed?

The atom with the lone pair donates a pair of electrons to the electron deficient atom that does not have a full outer shell of electrons

Bond Areas

In a double or triple bond

2 Bond pairs and 0 Lone pairs.

Linear shape

180 degrees

3 Bond pairs 0 lone pairs

Trigonal planar shape

120 degrees

4 Bond pairs 0 lone pairs

Tetrahedral shape

109.5 degrees

5 Bond pairs 0 lone pairs

Trigonal Bipyramidal shape

90 degrees and 120 degrees

6 Bond pairs 0 lone pairs

Octahedral shape

90 degrees

2 Bonding areas 0 lone pairs

Linear shape

180 degrees

3 Bonding areas 0 lone pairs

Trigonal planar shape

120 degrees

2 Bond pairs 1 lone pair

V-shaped/Non Linear shape

117.5 degrees

3 Bond pairs 1 lone pair

Trigonal Pyramidal shape

107 degrees

2 bond pairs 2 lone pairs

V-shaped shape

104.5 degrees

4 bond pairs 2 lone pairs

Square planar shape

90 degrees

Electronegativity

The power of an atom to attract the pair of electrons in a covalent bond

Across a period electronegativity…

Increases as there are more protons and similar shielding so stronger attraction between the nucleus and the electron pair in the covalent bond

The most electronegative atom is

Flourine

Down a group electronegativity…

Decreases as there is greater shielding and a larger atomic radius so there is a weaker attraction between the nucleus and the pair of electrons in covalent bond

Polar covalent bond

When there is an uneven distribution of electrons. The atom with the greater electronegativity attracts the bonding pair more and has a slightly negative charge. Must include O, N, F, Cl, I, or Br.

Non-polar covalent bond

No or very small difference in electronegativity. Atoms have the same electronegativity so the bonding pair is shared equally. Carbon and hydrogen have similar electronegativity so hydrocarbons are non-polar.

A molecule is non-polar if it is…

Symmetrical as the bond dipoles cancel

A molecule is polar if it is…

Asymmetric as the bond dipoles do not cancel

What are the types of intermolecular forces

Van der Waals forces, permanent dipole-dipole forces, hydrogen bonds

Van der Waals forces are caused…

By the movement of electrons which unbalances the charge distribution within the molecule. This creates an instantaneous dipole across the molecule that is constantly forming and disappearing. Inducing a dipole in neighbouring molecules, resulting in weak forces of attraction between molecules.

Van der Waals forces are present in…

All molecules but they are the only forces present between non-polar molecules

Bigger molecules have stronger van der waals forces because…

They have greater Mr so have more electrons so the induced dipoles are larger.

Permanent Dipole-Dipole Forces

Occur between polar molecules which have a permenant dipole, in addition to but stronger than Van der Waals forces. The positive dipole end of one molecule is attracted to the negative dipole end of a neighbouring molecule.

Hydrogen Bonding

Occurs between molecules which contain a hydrogen atom bonded to either F, O, N. A hydrogen bond is formed between a positive dipole H atom in one molecule and a lone pair of electrons on an N, O or F in a neighbouring molecule. The strongest intermolecular force.

Drawing hydrogen bonds…

Show two molecules, all lone pairs, partial charges, and partial alignment (H bond has to be a straight line with at least 3 atoms in line)

To change states…

Energy is needed to overcome the forces holding the particles together. The stronger the forces, the more energy is needed, the higher the melting or boiling point

An electric current can only flow…

If there are charged partices which are free to move. Current can be carried by delocalised electrons or free ions.

Substances can dissolve if…

Solute and solvent molecules attract one another.

Ionic and polar substances dissolve in

polar solvents

Non-polar substances dissolve in

Non polar solvents

Ionic compound

Giant ionic lattice, ionic bonding, strong electrostatic forces of attraction between oppositely charged ions.

Ionic solids conductivity?

Don’t conduct as the ions are fixed in position in the lattice so cannot move and therefore don’t carry charge

Dissolved or molten ionic conductivity?

Can conduct as ions become free to move and carry current so molten or dissolved ionic substances conduct

When enough force is applied to ionic substances…

The layers slide over one another. Ionic substances are brittle, so like charges move next to each other causing repulsion as the lattice structure breaks down

Ionic substances are generally…

Soluble in water, so positive ions attract the negative dipole in O, the negative ions attract the positive dipoles in H2

Metallic structure

Giant metallic lattice, bonding is metallic, strong forces of attraction between delocalised electrons and positive ions.

Why do metals have high melting points?

It takes a lot of energy to overcome the strong forces of attraction between positive ions and delocalised electrons

Why do metals conduct?

Because the delocalised electrons can move through the structure and carry the current

Why are metals strong?

Metals have strong forces of attraction between positive ions and delocalised electrons

Why are metals malleable and ductile?

The layers of ions in the giant metallic lattice can slide over each other into new positions without disrupting the metallic bond and the attraction between positive ions and delocalised electrons remains.

what are the types of covalent substances

Macromolecular and simple molecular

Melting point of covalent substances…

is low because intemermolecular forces are weak, so less energy is required to break the forces

Solubility of covalent substances

Non polar molecules dissolve in non polar solvents, they form van der Waals forces with solvent molecules. Polar molecules dissolve in polar solvents (eg H2O if they can form hydrogen bonds with water)

Conductivity of covalent substances

Don’’t conduct as the lattice doesn’t contain mobile electrons/ions (charged carriers) that are free to move

Substances with hydrogen bonding have…

Higher boiling points than expected due to the strength of the hydrogen bond between molecules. Tends to dissolve in water because they form hydrogen bonds with water

What are the anamalous properties of water?

Ice is less dense than water as hydrogen bonds hold neighbouring molecules far apart in an open lattice in ice. Water has a higher boiling point than expected. Forms more hydrogen bonds than eg NH3, as N has one lone pair, O has two lone pairs.

What is different about H2O, HF, NH3?

They have hydrogen bonds that are stronger than Van der Waals forces, so more energy is needed to overcome the hydrogen bonds between molecules

Boiling point trend down a group…

Increasing, as there are more electrons and higher Mr, there are stronger Van der Waals forces, so more energy is required to overcome them

What sort of bonds does carbon form and how many?

Four covalent bonds

Structural formula

Shows how the atoms in a molecule are arranged

Displayed formula

Shows all the atoms and bonds in a molecule

Skeletal formula

Shows the shape of the carbon skeleton

Homologous series

A family of compounds containing the same functional group and having the same general formula but having a different carbon chain length, each successive member has an extra CH2

Functional group

AN atom or group of atoms which gives an organic compound its chemical properties

List all 10 homologous series in order of increasing priority when naming

Halogenoalkanes, alkenes, amines, alcohols, ketone, aldehyde, nitrile, acyl chloride, ester, carboxylic acid, alkane

Suffix and functional group of amines?

-amine and -NH2

Suffix and functional group of ketones

-one

Suffix and functional group of aldehydes

-al

Suffix and functional group of nitriles

-nitrile

Suffix and functional group of acyl chlorides

-oyl chloride

Suffix and functional group of esters

-oate

Suffix and functional group of carboxylic acid

-oic acid

Hydrocarbons

Compounds containing carbon and hydrogen atoms only

Saturated hydrocarbons

Contain single carbon-carbon bonds only

Unsaturated hydrocarbons

Contains one or more carbon-carbon double bonds

Aliphatic hydrocarbons contains…

Chains

Alicylic hydrocarbons contains…

Rings

Aromatic hydrocarbons contains…

benzene rings