Section 1

Composition of Matter

• Matter is anything that occupies space and has mass.

• Elements are made of a single kind of atom and cannot be broken down by chemical means into simpler substances.

• Atoms are composed of protons, neutrons, and electrons. Protons and neutrons make up the nucleus of the atom. Electrons move about the nucleus in orbitals.

• Compounds consist of atoms of two or more elements

• Most elements react to form chemical bonds so that their atoms become stable. An atom achieves stability when the orbitals that correspond to its highest energy level are filled with the maximum number of electrons.

• A covalent bond is formed when two atoms share electrons.

• An ionic bond is formed when one atom gives up an electron to another. The positive ion is then attracted to a negative ion to form the ionic bond.

Vocabulary matter (p. 31) mass (p. 31) element (p. 31) atom (p. 32) nucleus (p. 32)

proton (p. 32) neutron (p. 32) atomic number (p. 32) mass number (p. 32) electron (p. 32)

orbital (p. 32) isotope (p. 32) compound (p. 33) chemical bond (p. 33) covalent bond (p. 33)

molecule (p. 33) ion (p. 34) ionic bond (p. 34)

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