Chemistry Review All living things are made up of atoms and it is the interaction of these atoms that is the foundation of life.

An element consists of one type of atom. What is an Atom? An atom is the smallest basic unit of matter that cannot be divided and maintain its physical and chemical properties. An element consists of one type of atom. All living things are made up of a variety of different atoms. H O Hydrogen atom (H) Oxygen atom (O)

Grade 9 Review Atoms on the periodic table have all the information about the subatomic particles that make up an atom. Atomic Number Na 23.0 11 Atomic Mass The atomic number tells you the number of ______________ Proton number dictate who an atom is. Since it is an atom and atoms are neutral ____________ and __________ have the same number. The atomic mass is made up of __________ and _________ as they are the only particles that have a significant mass. Protons Protons Electrons Protons Neutrons

Where Do These Particles “LIVE”? Protons and neutrons reside in the nucleus in the centre of the atom. Electrons are in energy levels outside the nucleus. It is the Electrons that are involved in chemical reactions. Oxygen atom (O) Nucleus: 8 protons (+) 8 neutrons outermost energy level: 6 electrons (-) inner energy level: 2 electrons (-) yh

How many Valence Electrons does an Element have? Lewis Diagrams Lewis Diagrams only show the outer electrons of an atom. Only valence electrons are involved in chemical reactions Only valence electrons are involved in forming bonds How many Valence Electrons does an Element have? Number of valence electrons of a main (A) group atom = Group number

Compounds A compound is made of two or more atoms of different elements bonded together. O H _ + water (H2O) A molecule consists of two or more of the same or different elements bonded together. - Oxygen (O2)

Why do Elements Bond? All elements want to look like the Noble Gases The Noble Gases are very stable and don’t react. This is due to their full outer shell. Atoms will gain, lose or share electrons in order to obtain a full outer shell (octet). Bonds are classified based on the method employed to reach a stable octet. There are two main types of bonds which are Ionic Bonds and Covalent bonds.

An ion is an atom that has gained or lost one or more electrons. Ionic Compounds An ion is an atom that has gained or lost one or more electrons. positive ions LOSE electrons negative ions GAIN electrons Ionic bonds involve the exchange of electrons. The bond is the electrostatic (opposite charges) attraction between the oppositely charged ions after the exchange. Sodium atom (Na) Chlorine atom (CI) Sodium ion (Na+) Chloride ion (CI-) Na loses an electron to CI ionic bond gained electron

Covalent Compounds A Covalent compound is made of atoms that SHARE their electrons to obtain a stable octet. This sharing is accomplished by an orbital overlap, (show below using the Bohr Model) Examples: - water (H2O) carbon dioxide (CO2)

Sharing……..is it always equal?  Not all covalent bonds share electrons equally  this means that the electrons being shared are more attracted to one atom in a bond and thus lean towards that atom more than the other Polar Covalent Bond: An unequal sharing of electrons that leads to partial charges on the atoms involved in the bond  How do you know if electrons are not being shared equally?

Polar Covalent Bonds and Electronegativity Answer: Electronegativity Electronegativity: Electronegativity is a measure of the tendency of an atom to attract a BONDING pair of electrons.

How to Determine Polarity of a Bond! 1. Draw the two atoms involved in the bond 2. Find the electronegativity for each element on the Periodic Table. 3. Find the DEN for the elements, (this value is always positive) 4. Analyze the results as follows:   DEN > 0.5 Polar Covalent Bond DEN < 0.5 Pure Covalent Bond (Non-polar Bond) 5. If the bond is polar covalent then write the partial charges above the elements. If the bond is pure covalent then there is no charge separation. d+ d- C – F

Polar Molecules Polar Molecules: Polar molecules are covalent compounds that have a slightly positive charge at one end (of the molecule) and a slightly negative charge at the other end (of the molecule)   When considering the polarity of a molecule, one must consider 2 things:   1. The DEN 2. The SHAPE or SYMMETRY of the molecule. Non-Polar Molecules: Non-Polar molecules are covalent compounds that have no charged ends.