The Nature of Matter Elements are made up of similar pieces of matter called atoms – The belief in atoms as the basic building block of matter dates back o the Greek philosophers (450 BC) when Democritus first proposed the existence of atomos (small particles of matter). Atoms are the smallest particle of an element retaining all of its properties. – Elements are listed on the periodic table by increasing atomic # in periods (rows) and by repeating chemical properties in groups and families (columns)

Atoms Atoms in an element are identical but different from atoms in other elements Atoms cannot be destroyed or created by physical or chemical reactions Atoms can be chemically joined to make compounds Atoms are made of even smaller subatomic particles called protons, neutrons, and electrons.

Sub-atomic Particles protons - have a positive charge, found in the nucleus and have an atomic weight of one – The number of protons determines the positive charge of the atom – The number of protons determines the atoms identity, called the atomic number – Mass is 1 amu electrons - have a negative charge, move in the space around the nucleus, and they have no appreciable mass – No appreciable mass or 1/1840 the mass of a proton – In neutral atoms the # of protons = # of electrons neutrons - have no net charge, found in the nucleus, and have an atomic weight of one – Atomic mass – atomic # = protons – Mass is 1 amu

Ions Whenever an atom gains or loses electrons it becomes an ion. You can find the net charge of the atom by subtracting the number of electrons from the atomic number. – If the result is positive (atomic # > electrons) - cation - overall positive charge example: Ca 20(p) - 18(e) = 2+ or Ca 2+ – If the result is negative (atomic # < electrons) - anion - overall negative charge example: O 8(p) - 10(e) = 2- or O 2-

Isotopes Isotopes have the same number of protons and electrons but differ in the number of neutrons. (mass - protons = neutrons) – Most elements in the first two rows of the periodic table have at least two known isotopes. – The isotope found most in nature is stable and all others are radioactive (unstable) Used in radioactive dating Example: hydrogen-1 hydrogen-2 hydrogen-3

Ionic Bonding Ionic bonds are formed from the transfer of electrons from one atom to another. The Ionic bond that forms is the result of the attraction of oppositely charged ions (atoms). The electrostatic attraction acts much like the opposite poles of a magnet. Here are some simple rules for ion formation and naming. – Ionic compounds consist of entirely ionic bonds (oppositely charged ions) – The ionic compound is electronically neutral (positive charges = negative charges) – Ions and ionic compounds are frequently more stable than their parent atoms – ionic compounds are made from a metal and a nonmetal

Covalent Bonding A covalent bond is one where the electrons are shared. A group of covalently bonded atoms is called a molecule. These molecular substances include DNA, sugar and carbon dioxide. The molecules can contain as few as 2 atoms and as many as a million. Rules for covalent bonds: – electrons are shared in covalent molecules – covalently bonded molecules follow the octet rule (some exceptions - BF 3 ) – covalent molecules can form single, double, or triple bonds – covalent bonds can be rearranged to form different molecules (glucose, fructose, & maltose)

Molecules and Compounds Molecules are made entirely of non-metals forming covalent bonds – Can have an overall charge and be classified as an ion (SO 4 2- ) Compounds are made entirely of oppositely charged ions – Dissolve in water to form electrolytes Elements, molecules, and compounds are considered pure substances as they cannot be physically altered and contain atoms in fixed ratios Mixtures are groups of elements, compounds, and/or molecules physically combined – Can be physically separated and are not considered pure – Can be combined using van der Waals forces … attraction by virtue of overall charge or electron arrangement. Weaker than covalent or ionic bonding