Elements, Mixtures and Atoms

• An element is a pure substance consisting of only one type of atom.
• Substances can be classified as either elements or compounds.
• The periodic table provides the symbols and names of all known elements.
• Chemical reactions can be described using word equations.
• Mass is always conserved in a chemical reaction.
• A mixture is a combination of two or more substances that are physically combined.
• Mixtures are different from compounds because they are not chemically bonded.
• Various separation techniques exist for separating mixtures.
• Fractional distillation is used to separate liquids with different boiling points.
• Paper chromatography is a technique used to separate substances.
• Several models have been proposed for the structure of atoms.
• The plum pudding model and the nuclear model are significant models of the atom.
• Atoms have no overall charge, making them neutral.
• An ion is an atom or molecule with an electrical charge due to the loss or gain of electrons.
• An isotope is a variant of an element with a different number of neutrons.
• Atoms are much larger than their nucleus.
• Electrons are found in specific energy levels within an atom.
• The first three energy levels can hold a maximum number of electrons: 2, 8, and 8, respectively.

Subatomic Particles

• Subatomic particles include protons, neutrons, and electrons.
• Relative charges: Protons (+1), Neutrons (0), Electrons (-1).
• Relative masses: Protons (1), Neutrons (1), Electrons (negligible).