• The?atomic number?(or?proton number) is the number of protons in the nucleus of an atom and has the?symbol?Z
  • The atomic number is also equal to the number of electrons that are present in a?neutral atom?of an element
  • E.g. the atomic number of lithium is 3, meaning that a neutral lithium atom has 3 protons and, therefore, also has 3 electrons
• The?mass?number?(or?nucleon?number) is the total number of?protons?+?neutrons?in the nucleus of an atom, and has the??symbol?A
• The number of?neutrons?can be calculated by:

Number of neutrons = mass number - atomic number

• • Protons and neutrons are also called?nucleons, because they are found in the nucleus

• Isotopes are atoms of the?same?element?that contain the same number of?protons?and electrons but a different number of?neutrons
• The way to represent an isotope is to write the?chemical?symbol?(or the?word) followed by a?dash?and then the?mass?number
  • E.g. carbon-12 and carbon-14 are isotopes of carbon containing 6 and 8 neutrons respectively
  • These isotopes could also be written as?12C or C-12, and?14C or C-14 respectively

The atomic structure and symbols of the three isotopes of hydrogen

• An atom is?neutral?and has no overall charge
• Ions on the other hand have either?gained?or?lost?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

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 - the number of protons does not change when an ion is formed

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 the number of protons, 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

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)

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