1.4 Chemistry Basics Part I SBI3C Mrs. Jones

Chemistry Basics  Biology is the study of living things  All living matter is composed of chemical substances  Matter is anything that has mass and takes up space

 Matter is composed of tiny particles called atoms.  All atoms are composed of subatomic particles: electrons, protons and neutrons. Chemistry Basics Protons (p+) and neutrons (n°) = nucleus Electrons (e-) = shells that orbit the nucleus

Chemistry Basics Neutral charge Located in the nucleus Positive charge Located in the nucleus Negative charge Orbits around the nucleus

 Pure elements are composed of the same atom.  All elements on the periodic table are organized according to their atomic mass. Chemistry Basics Do you notice a pattern? What is happening to the size of the atom?

Chemistry Basics Remember! Positive charges attract negative charges. The more protons (positive charge) the more the electrons (negative charge) are pulled towards the nucleus.

# of neutrons = Mass – Atomic Number Chemistry Basics 6 C Carbon Mass Number = protons + neutrons Symbol Atomic Number = # of protons = # electrons

Chemistry Basics How are the electrons arranged around the nucleus? 1 st shell = maximum of 2 electrons All other shells = maximum of 8 electrons Carbon has a total of 6 electrons: 1)Add the first two electrons in the first shell. 2)Add the remaining 4 electrons on the second shell. Is carbon a stable molecule? Explain your reasoning

 Each column in the periodic table consists of a specific group of elements that have the same number of valence electrons.  Example: Group 1, all of the elements have 1 valence electron. Chemistry Basics Are these elements reactive or non-reactive? Explain.

Chemistry Basics

 The chemical behaviour of an atom depends mostly on the number of electrons in its outermost shell.  All atoms with incomplete valence shells are chemically reactive. Chemistry Basics

The halogens are non reactive due to its full valence shell

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to H would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons Gain 1 electron Chemistry Basics

 Atoms form chemical bonds when they gain or lose an electron.  When the valence shell isn’t full, an element is reactive.  It wants to fill its valence shell in order to be stable.  In order to fill the valence shell, elements either lose, gain or share electrons. Intramolecular Bonds

Intramolecular bond: bond between two atoms that make a compound. Compound is made up of two or more atoms. Intramolecular Bonds 2 Types of Chemical Bonds Ionic Bonds Covalent bonds

 Ionic Bond: When electrons are transfered between a metal and non metal.  Metals and non metals come together to fill their valence electrons and become stable Ionic Bond

metals Non- metals Ionic Bond

 The atom that loses an electron has a positive charge and is known as a cation.  The atom that gains an electron has a negative charge and is known as an anion. Ionic Bond

 The opposite charges causes the ions to attract one another which results in a lattice Ionic Compound ( Na + Cl - ) Salt crystals Ionic Bond

 Covalent Bond: two atoms share their electrons.  The bond can be single, double or triple. Chemistry Basics

Single covalent bond Double covalent bond Four single covalent bonds Two single covalent bonds

2 Types of Covalent Bonds Polar CovalentNon-polar covalent Equal sharing of electrons Unequal sharing of electrons Determined by the atoms ELECTRONEGATIVITY E.g., H 2, O 2 E.g., H 2 O

 Electronegativity: the measure of the relative abilities of bonding atoms to attract electrons. Electronegativity = Stronger pull of shared electrons Electronegativity

You must take the electronegative difference between both atoms and compare it to the pauling scale to determine the type of bond.

 In a non-polar covalent bond, there is no electronegative difference. Electrons are shared equally.  E.g., O 2 oxygen atoms have the same electronegativity Formation of H 2 Formation of O 2 Electronegativity

 In a polar covalent bond, there is an electronegative difference. Electrons are shared unequally.  E.g., H 2 O oxygen atom is more electronegative than the hydrogen atoms Oxygen is more electronegative than hydrogen. Thus it has a tendency to pull the electrons closer to its own nucleus. Electronegativity

Oxygen now has more electrons surrounding its nucleus, thus giving it a partial negative charge. Hydrogen does not have as many electrons (less negative charge) and thus has a partial positive charge. Electronegativity

 Polar Molecules (like water) have an unequal distribution of charge.  Since water is polar, it can attract other water molecules.  The attraction between water molecules are called hydrogen bonds. Oxygen and nitrogen are common electronegative atoms that contribute to the formation of H-bonds in living cells. Polar Molecules