Grade 7 - Science Structure of the Atom

Grade 7 - Science

Structure of the Atom

Atoms are made up of a positively charged nucleus surrounded by one or more negatively charged electrons. These electrons orbit the nucleus.

The electron
The electron is a very tiny particle. Electron carries one unit of negative electric charge called -e

The nucleus
Unlike the electron, the nucleus can be broken up into smaller building blocks called protons and neutrons.
Together, the protons and neutrons are called nucleons.

The proton
Each proton carries one unit of positive electric charge. Since we know that atoms are electrically neutral.
The total positive charge of a nucleus is equal to the number of protons in the nucleus
The neutron
The neutron is electrically neutral i.e. it carries no charge at all.

Atomic number and Atomic mass
The number of protons in an atom.
You can find the atomic number on the periodic table (see periodic table at front of book). The atomic number is an integer and ranges from 1 to about 118.
The mass of an atom depends on how many nucleons its nucleus contains. The number of nucleons, i.e. the total number of protons plus neutrons, is called the atomic mass number and is denoted by the letter A.

Isotope
one of two or more species of atoms of a chemical element with the same atomic number and position in the periodic table and nearly identical chemical behavior but with different atomic masses and physical properties. Every chemical element has one or more isotopes.