Chemistry Basics: Elements, Compounds, and Mixtures

Elements

• 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.

Compounds

• 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).

Mixtures

• 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.

Atomic Structure

• 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.

Subatomic Particles

• Proton: relative mass of 1, charge of 1+
• Neutron: relative mass of 1, neutral charge
• Electron: relative mass of 1/1840, charge of 1-

Atomic Number

• 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.