Atomic Structures and Isotopes

Understand that atoms are composed of neutrons, protons and electrons.
Understand that elements are defined by the number of protons in their nucleus.
Understand that the atomic number of an element is the same as the number of protons in its nucleus.
MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.

Guiding Ideas

Lesson 6

Atoms are composed of electrons, protons and neutrons. The protons and neutrons form the atom's nucleus, this makes up the majority of the atom's mass. An electron is 2000 times smaller than a proton or neutron, however they take up most of the space in an atom.

Electrons form clouds around the nucleus, when elements react it is the electrons from two or more atoms that are interacting. So an element's electron configuration dictates its chemical properties.

An element has the same number of protons and electrons. The atomic number of the element is the same as the number of protons it has. The atomic mass of an atom is the sum of the mass of all its protons, neutrons and electrons.

The number of neutrons in an atom can vary. For example hydrogen has 3 forms, called isotopes. The most common form has 1 proton, no neutrons and 1 electron. Another from (isotope) of hydrogen, called deuterium, has 1 proton, 1 neutron and 1 electron. Tritium is also an isotope of hydrogen and has 1 proton, 2 neutrons and 1 electron.

Isotopes have the same chemical properties as each other, but different physical properties. e.g. they have different masses, some isotopes may be stable, whilst others may be radioactive.