• An atom is?neutral?and has no overall charge
• Ions on the other hand are formed when atoms either?gain?or?lose?electrons, causing them to become?charged
• The number of?subatomic particles?in atoms and ions can be determined given their atomic (proton) number, mass (nucleon) number and charge

Protons

• The atomic number of an atom and ion determines which element it is
• Therefore, all atoms and ions of the?same element?have the same number of protons (atomic number) in the nucleus
  • E.g. lithium has an atomic number of 3 (three protons) whereas beryllium has atomic number of 4 (4 protons)
• The number of protons equals the?atomic (proton) number
• The number of protons of an?unknown?element can be calculated by using its mass number and number of neutrons:

Mass number = number of protons + number of neutrons

Number of protons = mass number - number of neutrons

Worked example: Determine the number of protons

Answer

• Answer 1:?The atomic number of a magnesium atom is 12 suggesting that the number of protons in the magnesium element is 12
  • Therefore the number of protons in a?Mg²⁺?ion?is also 12
• Answer 2:?The atomic number of a carbon atom is 6 suggesting that a?carbon atom?has 6 protons in its nucleus
• Answer 3:?Use the formula to calculate the number of protons

Number of protons = mass number - number of neutrons

Number of protons = 63 - 34

Number of protons = 29

• • Element X?is therefore copper

Electrons

• An atom is?neutral?and therefore has the?same?number of?protons?and?electrons
• Ions have a different number of electrons to their atomic number depending on their charge
  • A positively charged ion has?lost?electrons and therefore has?fewer?electrons than protons
  • A negatively charged ion has?gained?electrons and therefore has?more?electrons than protons

Worked example: Determine the number of electrons

Answer

• Answer 1:?The atomic number of a magnesium atom is 12 suggesting that the number of protons in the?neutral?magnesium?atom?is 12
  • However, the 2+ charge in Mg²⁺?ion suggests it has?lost?two electrons
  • It only has 10 electrons left now
• Answer 2:?The atomic number of a carbon atom is 6 suggesting that the?neutral?carbon?atom?has 6 electrons orbiting around the nucleus
• Answer 3:?The number of protons of element?X?can be calculated by:

Number of protons = mass number - number of neutrons

Number of protons = 63 - 34

Number of protons = 29

• • The?neutral atom?of element?X? therefore also has 29 electrons

Neutrons

• The?mass?and?atomic?numbers?can be used to find the number of?neutrons?in?ions?and?atoms:

Number of neutrons = mass number (A) - number of protons (Z)

Worked example: Determine the number of neutrons

Answer

• Answer 1:?The atomic number of a magnesium atom is 12 and its mass number is 24

Number of neutrons = mass number (A) - number of protons (Z)

Number of neutrons = 24 - 12

Number of neutrons = 12

• • The?Mg²⁺?ion?has 12 neutrons in its nucleus
• Answer 2:?The atomic number of a carbon atom is 6 and its mass number is 12

Number of neutrons = mass number (A) - number of protons (Z)

Number of neutrons = 12 - 6

Number of neutrons = 6

• • The?carbon atom?has 6 neutrons in its nucleus
• Answer 3:?The atomic number of an element?X?atom is 29 and its mass number is 63

Number of neutrons = mass number (A) - number of protons (Z)

Number of neutrons = 63 - 29

Number of neutrons = 34

• • The?neutral atom?of element?X?has 34 neutrons in its nucleus