Atoms are the smallest part of an element and they are the basic building block of matter.
An atom has a nucleus in the centre, which contains protons and neutrons. The nucleus has an overall positive charge because protons have a positive charge and neutrons have no electric charge. Negatively charged electrons orbit the nucleus and they are arranged in a series of energy levels that are at specific distances from the nucleus.
Atoms have no overall charge. Electrons are negative and the nucleus is positive overall, so these charges cancel out. The table below shows the properties of these particles:
|Subatomic particle||Relative charge||Relative mass||Location|
|Electron||-1||1/2,000 (close to 0)||Electron shells around the nucleus|
Protons and neutrons make up nearly all of an atom’s mass. The radiuses of the electron orbits are far bigger than the radius of the nucleus. This means that most of the atom’s volume is empty space.
An element is defined by the number of protons in its nucleus, which means that atoms of the same element have the same number of protons. This is also the atomic number of the atom.
The mass number and the atomic number of an element can be shown like this:
In a stable atom, the number of protons is equal to the number of electrons. This means the overall electrical charge of an atom is 0. However, if an atom becomes ionised, the atom will lose or gain electrons.
Electrons in an atom are arranged in different energy levels, which are at different distances from the nucleus. We often call these energy levels shells and each shell gets progressively further away from the nucleus.
Electrons tend to stay at one energy level. However, with just the right amount of energy, an electron can jump to a higher energy level in its excited state. This energy comes from electromagnetic radiation. Although, this is followed by electrons dropping to a lower energy level and emitting electromagnetic radiation.
Electrons in higher energy levels have greater potential energy due to the greater distance between the electron and the nucleus.