Atomic Structure: Answers

Name the two subatomic particles that are found in the nucleus and state their charges.

The nucleus is made up of protons and neutrons. Protons are positively charged and neutrons have no charge (they are neutral).

What does atomic number represent?

The atomic number (the smaller number) tells us the number of protons in the nucleus of that atom. Since the number of protons is equal to the number of electrons (in a neutral atom), then it also tells us the number of electrons around the nucleus.

Why do atoms have an overall neutral charge?

Protons have a positive charge while electrons have a negative charge. Atoms have the same number of electrons as they have protons so the positive charges exactly cancel out the negative charges, resulting in a neutral atom.

Sodium (Na) has an atomic number of 11 and a mass number of 23. State the number of protons, neutrons and electrons in a sodium atom.

Short answer: 11 protons, 12 neutrons, 11 electrons

Long answer: The atomic number tells us the number of protons, so we know that sodium has 11 protons in its nucleus. Number of protons = number of electrons so there are also 11 electrons outside the nucleus. The mass number tells us the number of protons and neutrons so we can do mass number - atomic number to find out the number of neutrons alone. 23 - 11 = 12 so there are 12 neutrons in the nucleus.

What is an isotope?

Isotopes are atoms of an element with the same number of protons but different numbers of neutrons. An example would be carbon-12 and carbon-13, both of which have 6 protons in their nucleus but carbon-13 has an extra neutron compared to carbon-12.

A sample of bromine contains 45% bromine-79 and 55% bromine-81. Calculate its relative atomic mass (RAM).

RAM = (mass x percentage of isotope 1) + (mass x percentage of isotope 2) / 100

RAM = (45 x 79) + (55 x 81) = 80.1