2. Atoms, elements and compounds

What is an element?

A substance made up of only one type of atom which cannot be split into anything simple

What is a compound?

Pure substance made up of 2 or more elements chemically combined

What is an element?

A substance made up of only one type of atom which cannot be split into anything simple

What is a compound?

Pure substance made up of 2 or more elements chemically combined

What is a mixture?

A combination of 2 or more substances physically, not chemically

Can be separated physically(filtration, evaporation)

Describe the structure of an atom

Central nucleus containing neutrons and protons surrounded by shells of electrons

What is the relative charge and relative mass of a proton?

Relative charge= +1

Relative mass= 1

What is the relative charge and relative mass of a neutron?

Charge= 0

Mass= 1

What is the relative charge and relative mass of an electron?

Charge= -1

Mass= 1/2000

What is the atomic number?

Amount of protons in the nucleus of an atom

Smallest number on periodic table

What is nucleon number?

Total amount of protons and neutrons in the nucleus of an atom

How to determine how many shells an element has in electronic configuration?

Period number/row number

How to determine how many outer shell electrons an element has?

Group number of element

Eg: O is in grp 6, therefore has 6 outer electrons

What is a noble gas?

An element which has 8 outer electrons

All grp 8 elements r noble gases

What is an isotope?

Different atoms of the same element which has:

• Same proton number

• Different amount of neutrons

• Same number of electrons

Why do isotopes of the same element have same chemical properties?

Because they have same number of electrons, therefore same electronic configuration

How to calculate relative atomic mass in %

Ar=[(%of isotope A x mass of isotope A)+(%of isotope B x mass of isotope B)]/100

How are cations formed?

Positive ions are formed when they lose electrons, so they have more protons than electrons

How are anions formed?

Negative ions are formed when they gain electrons, so they have more electrons than protons

What is ionic bonding?

A strong electrostatic attraction between oppositely charged ions

Describe dot and cross diagram

• Only outer electrons are shown

• Charge of ion is spread evenly, shown by using square brackets

• Charge of each ion is written on top right corner

Describe the giant lattice structure of ionic compounds

(State which ions are present)

Regular arrangement of alternating positive and negative ions connected by strong electrostatic forces

What are the properties of ionic compounds

• High melting point and boiling point

• Good electrical conductivity when aqueous or molten

• Poor electrical conductivity when solid

Why do ionic compounds have high melting and boiling points?

The strong electrostatic forces known as ionic bonds require a lot of energy to break

Which is why ionic compounds have high mp and bp

Why do ionic compounds have poor conductivity when solid and high conductivity when liquid?

When solid, ions r fixed and cannot move, so they r poor conductors

When liquid, the ions can move and carry charge, therefore have high conductivity

Remember

When explaining properties, always state:

• Type of structure(lattice)

• Type of bonds/forces(ionic bonds/electrostatic forces)

What is the relation between charges and strength of ionic bonds in ionic compounds?

Smaller charge=weaker ionic bond, therefore less energy required for bond breaking, lower mp

Bigger charge=stronger ionic bonds, therefore more energy required for bond breaking, higher mp