2.1 The Nature of Matter

 Basic unit of matter  May be broken into smaller particles that do NOT have the properties of the element.

 Very small- 100 million atoms would make a row only about 1 centimeter long  Consists of protons, neutrons, and electrons.

    Nucleus  Core of atom Protons  Positive charge, in nucleus, mass of 1 atomic unit Neutrons  No charge, in nucleus, mass of 1 atomic unit Electrons  Negative charge, orbits nucleus, mass of 0 atomic units (technically a mass of 1/1840).

 Atoms have equal numbers of electrons and protons, their positive and negative charges balance out, and atoms themselves are electrically neutral.

 Matter is made up of atoms  Atoms join together to make compounds  Compounds use chemical bonds to hold them together  Chemical bonds are stored energy  Molecule  Atoms of the same element joined together.

 Elements and isotopes have same number of electrons  All isotopes of an element have the same chemical properties.

 Pure substance that consists entirely of one type of atom or  Elements cannot be broken down into other types of substances  Mercury (Hg).

 Atoms of the same element that differ in the number of neutrons.

 Atomic number  Number of protons  Atomic Number (atomic mass or weight)  Number of protons and neutrons.

 Atomic Number  6  Mass Number  12

  Nuclei are unstable and break down at a constant rate over time Used for  Determine the ages of rocks and fossils by analyzing the isotopes found in them  Detect and treat cancer  Kill bacteria that cause food to spoil  Labels or “tracers” to follow the movements of substances within organisms.

 Substance formed by the chemical combination of two or more elements in definite proportions  Water, the chemical formula H 2 O, contains two atoms of hydrogen for each atom of oxygen.

    Physical and chemical properties of a compound can be different from the elements that forms it Sodium  Reacts explosively with cold water Chlorine  Very reactive, poisonous, greenish gas that was used in battles during World War I Sodium Chloride  Table salt.

     Attraction between two atoms resulting in a sharing or transferring of an electron(s) Uses electrons Covalent Bond  Chemical bond that SHARES electrons Ionic Bond  Chemical bond that TRANSFERS electrons Hydrogen Bond  Weak bond between hydrogen ions.

 Shares electron(s).

 Transfer of electron(s)  Ion  A charged particle  Protons do NOT equal electrons

 A sodium atom easily loses its one valence electron and becomes a sodium ion (Na + ).

 A chlorine atom easily gains an electron (from sodium) and becomes a chloride ion (Cl ).

 Slight attraction can develop between the oppositely charged regions of nearby molecules  Due to unequal sharing of electrons within each molecule  Much weaker than Covalent of Ionic bonds.