Chemistry Basics: Elements, Compounds, and Mixtures

Study Notes

An element is a substance made up of atoms with the same number of protons, and it cannot be split into simpler substances.
There are 118 elements found in the Periodic Table.

A compound is a pure substance made up of two or more elements that are chemically combined.
There is an unlimited number of compounds.
Compounds cannot be separated into their elements by physical means.
Examples of compounds include copper(II) sulfate (CuSO4), calcium carbonate (CaCO3), and carbon dioxide (CO2).

A mixture is a combination of two or more substances (elements and/or compounds) that are not chemically combined.
Mixtures can be separated by physical methods such as filtration or evaporation.
Examples of mixtures include sand and water, oil and water, and sulfur powder and iron filings.

All substances are made up of tiny particles called atoms, which are the building blocks of matter.
Each atom is made up of subatomic particles called protons, neutrons, and electrons.
The protons and neutrons are located at the centre of the atom, which is called the nucleus.
The electrons move very fast around the nucleus in orbital paths called shells.
The mass of an atom is contained within the nucleus where the protons and neutrons are located.
The size of atoms is very small, so a unit called the relative atomic mass is used to measure their mass.

The atomic number (or proton number) is the number of protons in the nucleus of an atom.
The symbol for atomic number is Z.
The atomic number is also the number of electrons present in a neutral atom and determines the position of the element on the Periodic Table.