Ch 14 & 15 (atoms & the periodic table) – Study Guide
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All matter is made of atoms.
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Atoms are made of protons, neutrons and electrons – called subatomic particles.
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Protons are positive, are found in the nucleus and have a mass of 1 amu.
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Neutrons have no charge, are in the nucleus and have a mass of 1 amu.
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Electrons are negative, are found outside the nucleus and have very small mass.
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Democritus coined the term atom in ancient Greece.
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John Dalton (early 1800s) is often called the father of modern chemistry.
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JJ Thomson (late 1800s) discovered the electron using a cathode ray tube.
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Ernest Rutherford (gold foil) discovered that the atom is mostly empty space.
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Niels Bohr (early 1900s) explained energy levels of electrons.
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Modern theory uses the electron cloud model.
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Atomic number is the number of protons. Can be found on the periodic table.
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Mass number is the number of protons and neutrons in an atom.
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Atomic mass (or atomic weight) is the average mass of all isotopes of an element.
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Atomic mass (or atomic weight) almost always has decimals.
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Isotopes are atoms of the same element with different numbers of neutrons.
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13C
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Ions are atoms that have gained or lost electrons and have an electrical charge.
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Neutral (no charge) atoms have the same number of protons as electrons.
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+ ions have lost electrons. – ions have gained electrons.
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Most of the periodic table is metals.
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A zig-zag line separates the metals (left) from the non-metals (right).
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Along the zig-zag line are the metalloids.
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Columns (up and down) are called groups or families
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Rows (left to right) are called periods.
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Elements in the same period have the same number of energy levels present.
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Elements in the same group have similar chemical properties.
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Elements in the same group have the same number of valence (outer) electrons.
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Some groups have special names (alkali metals, alkaline earth metals, halogens,
or carbon-13 = two ways to write mass number.
noble gases)