Post on 13-Dec-2015
Chemical Fundamentals Review
• Living things are composed of matter.
• Matter has mass, occupies space.
• Atoms composed of: – Small nucleus
• Proton (positive charge)• Neutron (no charge)
– Orbited by• Electrons in arranged in shells
(negative charge)
What is the PERIODIC TABLE?
o Shows all known elements in the universe.
o Organizes the elements by chemical properties.
How do you read the PERIODIC TABLE?
What is the ATOMIC NUMBER?
o The number of protons found in the nucleus of an atom
Oro The number of electrons
surrounding the nucleus of an atom.
What is the SYMBOL?
oAn abbreviation of the element name.
What is the ATOMIC WEIGHT?
oThe number of protons and neutrons in the nucleus of an atom.
How do I find the number of protons, electrons, and neutrons in an element using
the periodic table?
o # of PROTONS = ATOMIC NUMBER
o # of ELECTRONS = ATOMIC NUMBER
o # of NEUTRONS = ATOMIC _ ATOMIC WEIGHT NUMBER
Example
• Atomic Mass – 12• Atomic Number - 6• Protons (6)• Electrons (6)• Neutrons (12-6 = 6)
Bohr Rutherford Diagrams
1. Write how many protons and neutrons are in the nucleus.
2. Draw electrons in rings (energy shells) around the nucleus.
Ex. Fluorine 19 F9
9p+10 n
Bohr- Rutherford Diagrams
1. Write the # of protons and neutrons in the nucleus.
2. The 1st electron energy shell has a maximum of 2 electrons.
3. The 2nd electron energy shell has a maximum of 8 electrons.
4. The 3rd electron energy shell has a maximum of 8 electrons.
18p+
22n0
Argon
Why are Electrons so Important?
The chemical behaviour of an atom depends mostly on the number of electrons in its outermost shell. valence electrons/shell
All atoms with incomplete valence shells are chemically reactive and are responsible for the formation of chemical bonds between atoms.
Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to N would like toO would like toH would like to
Gain 4 electronsGain 3 electronsGain 2 electronsGain 1 electron
Atoms bond to form compounds
• Compounds are made up of at least 2 different kinds of atoms (e.g., H2O)
• Bonds are formed by the sharing or transfer of electrons
2 Types of Chemical Bonds
Ionic Bonds
Covalent bonds
Ionic Bonds – occur when one atom donates or gives up one or more
electrons- metal and non metal
Ionic Compound ( Na+Cl-) Salt crystals
Opposite charges
attract to form ionic
bonds
Covalent Bonds – involve a sharing of a pair of valence electrons between atoms between two non-metals
Single covalent bond
Double covalent bond
Four single covalent bonds
Two single covalent bonds
2 Types of Covalent Bonds
Polar Covalent Non-polar covalent
Equal sharing of electrons
Unequal sharing of electrons
Determined by the atoms
ELECTRONEGATIVITY
E.g. H2O2
E.g. H2O
Electronegativity•The measure of an atom’s attraction for additional electrons
•Polar Covalent Bond - unequal sharing of electrons between two atoms with different electronegativity results.
•Non-Polar Covalent Bond – equal sharing of electrons between two atoms.
Electronegativity = Stronger pull of shared electrons
The electronegativity difference (∆En) is the difference in electronegativity number between two atoms participating in a covalent bond.
Electronegativity Differences
Most Biological compounds contain: Carbon, Oxygen, Hydrogen, and NitrogenOxygen and Nitrogen form polar bonds with atoms of most other elementsCarbon and Hydrogen bonds are generally considered non-polar
Molecular Polarity• Depends on – Distribution of charges – Molecular shape
• Symmetrical molecular shapes produce non-polar molecules (whether bonds are polar or not)
• Asymmetrical molecular shapes produce polar molecules
• Balanced charges produce non-polar molecules
• Non-balanced charges produce polar molecules
Polar Molecules• Align themselves
to other polar molecules
• Soluble in water
• Exclude non-polar molecules (oils and fats)
VSEPR• Valence shell electron pair repulsion
• Electrons repel one another forming the shape of the molecule
• Includes both bonded electron pairs and non-bonding electron pairs (lone pairs)
VSEPR