BTEC applied science Chemistry

Ion

An atom or group of atoms that has a positive or negative charge.

Nitrate

NO3-

Carbonate

CO3 2-

Sulfate

SO4 2-

Hydroxide

OH-

Ammonium

NH4+

Zinc

Zn2+

Silver

Ag+

Metals in group 1, 2 and 3 in the periodic table

Form 1+ 2+ and 3+ ions

Non-Metals in groups 5, 6 and 7

Form 3- 2- and 1- ions

If a molecule is covalent

8 - group number

Writing equations

1. Write the correct formula for all reactants and products

2. Check the numbers of each atom balance

3. Add state symbols if required

Electron pattern

1st shell = 2 electrons

2nd shell= 8 electrons

3rd shell= 18 electrons

4th shell= 32 electrons

5th shell= 50 electrons

Aufbau Principle

states electrons fill the orbital with the lowest available energy state in relation to the proximity in the nucleus before filling orbitals

Spin

electrons have two possible states, spin up or spin down. In an orbital each electron will be in a different spin state.

electron configuration

the arrangement of electrons in atoms or ions

Ionic bonds

Strong electrostatic attractions between positive and negative ions. Ions in ionic bonds shown in electron configuration diagrams

When does ionic bonding occur?

When an atom of an element loses one or more electrons donates it to an atom of a different element

Due to inbalance of protons and electrons

Atoms that lose electrons

positively charged

Atoms that gain electrons

Negatively charged

electrostatic attraction

force experienced by oppositely charged particles- holds particles strongly together

Smaller ions greater charge

Stronger the attractions is between negative and positive ions.

Strength of ionic bonding

Greater charge on the ions stronger the ionic bonding

Smaller the ions stronger ionic bonding (Ions get bigger down the group)

Formation of ions

All elements lowest energy- full shell of electrons

Ionisation energy

Distance from nucleus (atomic radius)

More positive- less electrons

Less positive further away negative more electrons

Nuclear charge

Shielding

Shielding

repulsion by electrons in inner shells between nucleus and outer electron

Positive ions

Generally formed by metal atoms - losing electrons

Positive charge equal to group number

Different charges if formed from transition metal e.g Fe2+ , Fe3+

Known as Cations

Negative ions

Formed by non-metal atoms gaining electrons from metal ions

Negative charge equal to 8 minus group number of element sometimes - polyatomic ions need to be learned

Known as Anions

Comparing strength of ionic bonds

Ionic charge and ionic radius be considered

e.g. MgF2 stronger than bonding NaF

Magnesion ion smaller than sodium ion- greater charge

Increase electrostatic attraction between the ions

Sodium chloride lattice

Each sodium ion surrounded by six chloride ions each chloride ion surrounded by six sodium ions

Pattern continues

Opposite charges ions in sodium chloride from giant ionic lattice ions arranged in a regular pattern

Strength electrostatic force ionic bonds depend on ionic charge and ionic redil of ions

More electrons a positive ion has- more shells it will have

If an ion- more shells radius- be bigger than an ion with fewer shells

Electrostatic force of attraction stronger ionic charge is higher

Covalent bonds

Electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atom

When do covalent bonds occur?

Between atoms of two non-metals. A covalent bond forms an electron is shared between the atoms. These electrons come from top energy levels of the atom.

Type of structure with covalent bonding

Simple molecular - part of a structure e.g. C2H6 (Ethane)

Giant covalent- Graphite

How do atoms form covalent bonds?

When atoms share a pair of electrons. Each atom in bond contributes one electron to the pair, a covalent bond consisting of more than one electron - shared- dative coordinate bond.

Strength of covalent bonds

Shorter the bond - stronger the bond is

Double bonds- stronger than single bonds, triple bonds stronger than double bonds

Covalent bonds are formed when

non-metal reacts with non-metal

bond length and bond strength are inversely related

Shorter bond length greater covalent bond strength

Atoms share electrons- stable electron structures (fill outer shells)

Two shared electrons make single bond, four shared electrons make a double bond, six shared electrons make a triple bond

Lone pairs

non-binding pair of electrons

e.g. on nitrogen when bonded with ammonium

Dative covalent bond

Both sharing electrons come from one atom

e.g ammonium ion

Forms double bonds

Between oxygen two pairs shared electrons

organic compounds

compound that contains one or more carbons in a carbon chain

Carbon four covalent bonds forms many compound

Methane CH4 Each carbon atom bonds covalently with four hydrogen atoms

Meaning methane not a flat molecule

Tetrahedral structure because bonds separated from one another as possible.

number of moles

Mass / Mr

mass

no of moles x Mr

Concentration

moles/volume

Percentage yield

actual amount in mol of product / theoretical amount in mol of product x 100