Structure of the Atom Learning Objective: To describe the structure of an atom To state the atomic numbers of elements To recall the relative charge and relative mass of elements

If a helium atom was the size of a full stop, then the average gerbil would be the size of the Earth. Atoms: very small

Most of the atom is empty space! If you imagine an atom being the size of Wembley stadium, the nucleus would be about the size of a football on the centre spot. The electrons would be two peas flying around the whole stadium. The rest of it: emptiness.

Atoms Atoms are incredibly tiny. It is not possible to see an individual atom, let alone see what is inside one. Atoms are the smallest particles of an element that can take part in chemical reactions. To understand their structure, scientists have concluded an even smaller object at its centre, called a nucleus. This is about times smaller than the atom itself.

Subatomic Particles Atoms are made from three types of subatomic particles. The nucleus contains protons and neutrons. It is surrounded by electrons. The electrons are arranged in shells (or energy levels) at different distances from the nucleus Subatomic particles have very, very small masses and electrical charges. It is more convenient to describe their masses can charges compared to a proton. These are called the particles relative mass and relative charge

Mass and Charge Subatomic Particle Relative Mass Relative charge Proton1+1 Neutron10 ElectronNegligible (1/1840)

Atoms and Elements Every atom of a particular element has the same number of protons in their atoms. For example, all hydrogen atoms contain one proton, all helium atoms contain two protons. This means that they have no overall charge.

Rules All atoms of an element have the same number of protons – they also have the same number of electrons. For example, all atoms of oxygen contain 8 protons in their nucleus with 8 electrons in the energy levels. All atoms of one element are different from all the atoms of other elements – they have different numbers of protons (and electrons).

Li 7 3 (No. of protons) No. of protons + neutrons Lithium Number of protons Number of electrons = Atomic number does not always equal the number of neutrons. Lithium Electrons3 Protons3 Neutrons4 Mass number Atomic number or proton number

Lithium Number of protons Number of electrons = Lithium Electrons3 Protons3 Neutrons4 This is because the atom is neutral. The charges balance out! -3 charge +3 charge But atoms can gain and lose electrons (they become ions). This changes the overall charge on the atom. We will do this later! No charge