Atomic Theory and Bonding p. 102 -124 Atoms are made up of smaller particles called subatomic particles. (c) McGraw Hill Ryerson 2007

The nucleus is at the centre of an atom. Parts of an Atom: The nucleus is at the centre of an atom. composed of protons and neutrons. electrons are in the space surrounding the nucleus. # of protons = # of electrons nuclear charge = charge on the nucleus = # of protons atomic number = # of protons = # of electrons (c) McGraw Hill Ryerson 2007

Evidence of a chemical reaction: Chemical Reactions a process in which atoms of one or more pure substances are rearranged to form new substances Evidence of a chemical reaction: Energy change ( change in temperature, produces light or sound) Change in colour Change in odour Bubbles form (indicates a gas is being formed) Solution becomes cloudy (precipitate forms) (c) McGraw Hill Ryerson 2007

Periodic Table and Ion Formation Atoms gain & lose electrons to form ionic bonds. become electrically charged particles (= ions) Metals lose electrons & become positive ions (= cations). Some metals (multivalent) lose electrons in different ways. Ex: iron, Fe, loses either two (Fe2+) or three (Fe3+) electrons Non-metals gain electrons & become negative ions (= anions). Atoms gain & lose electrons in an attempt to have the same number of valence electrons (= electrons in outermost shell) as the nearest noble gas. (c) McGraw Hill Ryerson 2007

Electrons appear in shells in a very predictable manner. Bohr Models Electrons appear in shells in a very predictable manner. There is a max. of 2 electrons in the first shell, 8 in the 2nd shell, and 8 in the 3rd shell. The period number = the number of shells Except for transition elements, the last digit of the group number = the number of electrons in the valence shell. The noble gas elements have full electron shells & are very stable (c) McGraw Hill Ryerson 2007

When two atoms get close, their valence electrons interact. Forming Compounds When two atoms get close, their valence electrons interact. If the valence electrons can combine to form a low-energy bond, a compound is formed. Two types of bonds: 1. Ionic bonds form ions when electrons are transferred from metals to non-metals usually, metals lose electrons & non-metals gain electrons the resulting charges keep the ions together 2. Covalent bonds form when electrons are shared between two non-metals electrons stay with their atom but overlap with other shells. NO ions are formed! (c) McGraw Hill Ryerson 2007

Forming Compounds (continued) Ex: lithium & oxygen form an ionic bond in the compound Li2O. Ex: hydrogen & fluorine form a covalent bond in the compound HF + lithium oxygen Electrons are transferred from the positive ions to negative ions Li+ O2- Li+ lithium oxide, Li2O + Hydrogen fluoride hydrogen fluorine electrons are shared (c) McGraw Hill Ryerson 2007

illustrate chemical bonding Lewis Diagrams illustrate chemical bonding show only an atom’s valence electrons & chemical symbol dots (= electrons) are placed around the element symbols at the points of the compass (N, E, S, & W). placed singly until the 5th electron is reached then they are paired. (c) McGraw Hill Ryerson 2007

can be used to represent ions & ionic bonds Lewis Diagrams of Ions can be used to represent ions & ionic bonds For + ions, one electron dot is removed from the valence shell for each positive charge. For - ions, one electron dot is added to each valence shell for each negative charge. Square brackets are placed around each ion to indicate electrons have been transferred. – 2+ – • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Be Cl Cl Be Cl Cl Be Cl Each beryllium has two electrons to transfer away, and each chlorine can receive one more electron. Since Be2+ can donate two electrons and each Cl– can accept only one, two Cl– ions are necessary. beryllium chloride (c) McGraw Hill Ryerson 2007

Lewis Diagrams of Covalent Bonds can also represent covalent bonds Like Bohr diagrams, valence electrons are drawn to show sharing of electrons. The shared pairs of electrons are usually drawn as a straight line. (c) McGraw Hill Ryerson 2007

Lewis Diagrams of Diatomic Molecules Diatomic molecules, like O2, are also easy to draw as Lewis diagrams. • • • • • • • • • • • • • • • • • • • • • • • • O O O O O O Several non-metals join to form diatomic molecules. Valence electrons are shared, here in two pairs. This is drawn as a double bond. (c) McGraw Hill Ryerson 2007

Try these: Sodium + chlorine Phosphorus + fluorine Carbon + hydrogen Magnesium + nitrogen (c) McGraw Hill Ryerson 2007