Atomic Structure

After Periodic Table, we began on atomic structure. To help us in this topic, besides the usual notes, worksheet and assignment, we were also provided a powerpoint to help us digest all this infomation at home if we did not understand what the teacher was teaching in class. Here are some of the notes.

The number of protons in an atom is called the proton number. Proton number is also known as the Atomic Number.

Nucleon number is the number of protons and neutrons in the nucleus of an atom. Nucleon number is also called the Mass Number.

Nucleon (Mass) number = number of protons + number of neutrons

The centre of an atom is called the nucleus which contains the protons and neutrons.

The electrons in an atom are arranged in shells (orbits) at different distances from the nucleus.

Note: Shells are also called energy levels.

Each shell can hold a certain maximum number of electrons.
(a) 1st shell - 2 electrons
(b) 2nd shell - 8 electrons
(c) 3rd shell - 8 electrons
(1st 20 elements only)
Advanced: For elements after calcium in the 4th period, their third shell can hold up to 18 electrons.

An atom can be described as an electrically neutral entity made up of a positively charged nucleus at its centre with negatively charged electrons moving around the nucleus.

All atoms of the same element have the same number of protons while those of different elements contain different number of protons.

Isotopes are atoms of the same element with different numbers of neutrons.

Only valence electrons are involved in chemical reactions.

Following this topic on atomic structure, it would go further and touch on the formation on ions, as well as chemical bonding.