Elements, Compounds, and Mixtures

Elements, Compounds, and Mixtures

• An element is a substance made up of atoms with the same number of protons, and cannot be split into simpler substances.
• There are 118 known elements listed in the Periodic Table.
• A compound is a pure substance made up of two or more elements chemically combined, with an unlimited number of possible compounds.
• Compounds cannot be separated into their elements by physical means.

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 consists of protons, neutrons, and electrons.
• Protons and neutrons are found in the nucleus at the center of the atom, while electrons move rapidly around the nucleus in orbital paths called shells.

Subatomic Particles

• Protons have a relative mass of 1 and a charge of 1+.
• Neutrons have a relative mass of 1 and a charge of 0 (neutral).
• Electrons have a negligible mass (about 1/1840) and a charge of 1-.

Relative Atomic Mass

• The relative atomic mass is a unit used to measure the mass of atoms.
• One relative atomic mass unit is equal to 1/12th the mass of a carbon-12 atom.
• The relative atomic mass of an element is measured relative to the mass of a carbon-12 atom.

Atomic Number (Proton 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 determines the position of an element on the Periodic Table and is also the number of electrons present in a neutral atom.