Elements, Compounds and Mixtures

Elements, Compounds and Mixtures

Elements

  • An element is a substance that contains only one type of atom.

  • Elements cannot be broken down into simpler substances using chemical reactions.

  • The periodic table lists all known elements, which are classified as either metals, non-metals, or metalloids.

  • Each element has a unique atomic number, which is equal to the number of protons in its nucleus.

Compounds

  • A compound is a substance formed when two or more elements chemically combine.

  • Compounds have properties that are different from the elements they are made from. For example, hydrogen and oxygen are gases at room temperature, but when they combine to form water, the result is a liquid.

  • The ratio of atoms in a compound is always fixed. For example, water (H2O) always has two hydrogen atoms for every oxygen atom.

  • Compounds can be broken down into their constituent elements using chemical reactions, but not by physical processes.

Mixtures

  • A mixture is a combination of two or more substances that are not chemically combined.

  • The substances in a mixture can be present in any proportion. For example, air is a mixture that mostly consists of nitrogen and oxygen, with small amounts of other gases.

  • Mixtures can be separated into their component substances using physical processes like filtration, distillation, or chromatography.

  • The properties of a mixture are the sum of the properties of the individual substances in it. For example, air has the properties of all the gases it contains.

Atomic Structure

  • Atoms consist of a nucleus (containing protons and neutrons) surrounded by electrons in energy levels, also known as shells.

  • Protons carry a positive charge, electrons a negative charge, and neutrons no charge.

  • The number of protons in the nucleus of an atom is called its atomic number and this determines what element the atom is.

  • Electrons in the outermost shell of an atom are called valence electrons; they determine the element’s chemical properties and its ability to form bonds.

  • The combination of protons and neutrons in an atomic nucleus is known as its mass number.

NOTE: Always remember that atoms are not created or destroyed in chemical reactions, they are merely rearranged.