Combinations of Atoms Chapter 4.2 Page 87

Organization of the Periodic Table Each Box gives information about one element Name of element Atomic number (number of protons) Atomic Symbol Atomic Mass

Position shows electron arrangement Periods—horizontal rows Give number of electron shells used

Groups Groups—vertical columns Within a column elements have the same number of valence electrons

Atoms are the building blocks of molecules water molecule

Molecules The smallest unit of matter that can exist by itself and retain all of a substances chemical properties In a molecule two or more atoms are bonded together

Diatomic molecules di--two Some molecules are made of the same kind of atom O2

Ozone is O3

Chemical Formulas A combination of letters and numbers that shows the number of atoms of each element that are required to make a molecule of the compound

Chemical Equations Elements and compounds often combine through chemical reactions The reaction can be described in a formula

Photosynthesis formula 6H2O + 6CO2 -------> C6H12O6+ 6O2 Reactants on left products on right The arrow is read yields

Balanced equations An equation is balanced when the number of atoms on the right equals the number of atoms of the same element on the left To balance a formula you use coefficients

Photosynthesis formula 6H2O + 6CO2 -------> C6H12O6+ 6O2 What is the blue arrow pointing to? What is the red arrow pointing to?

CO2 H2O

Book example Magnesium, Mg, reacts with oxygen, O2, to form MgO, magnesium oxide Write a balanced equation. We have two oxygen on the right so we will need a number 2 on the left as a coefficient 2 Mg + O2 2MgO

Chemical Bonds chemical bonds The forces that hold together the atoms in molecules are called chemical bonds Bonds form because of attraction between opposite charges Atoms can share or transfer valence electrons

Ions When an electron is transferred from one atoms to another both atoms become charged A charged particle like an atom or molecule is an ion

Cat lover or cat hater

A positively charged ion is a cation (+)

A negatively charged ion is called an anion (-)

Ionic Bonds Attractive force between two oppositely charged ions that result from the transfer of electrons from one atom to another is called An ionic bond

Na from the left wants to give away Cl from the right wants to gain electrons Ionic bonds form from atoms from opposite sides of the periodic table

Covalent Bonds A bond between atoms that share electrons is called a covalent bond http://www.ithacasciencezone.com/chemzone/lessons/03bonding/mleebonding/covalent_bonds.htm

Polar Covalent Bonds Some atoms that are covalently bonded do not equally share elections A covalent bond with unequal attraction is called a polar covalent bond Water is one example

Metallic Bonds Electrons flow easily They are not tightly bound This explains the properties of metals

Electron From Greek word for amber Ben Franklin found electricity was a flow of electrons

Ben Franklin found electricity is the flow of electrons

Physical Change A change of matter from one form to another without a change in chemical properties Break Crush Melt 140

Change of State is a physical change An item can change from solid to liquid to gas and still have the same chemical formula 140

Dissolving is a physical change Example: dissolve salt in water You still have salt and water You could evaporate the water and get the salt back Something that dissolves is soluble 140

Chemical Changes Form new substances with different physical properties Can be detected Fizz Smell Color Produce heat Produce a sound Cannot be reversed by physical means 142

Exothermic—produce heat Endothermic—solution gets colder

Mixtures A combination of two or more substances that are not chemically combined Two types: Heterogeneous--different Homogenous--same

Heterogeneous mixtures Two or more substances are not uniformly distributed Example Granite

Homogenous mixture Having the same composition throughout

Solution A homogenous mixture of two or more substances that are uniformly dispersed When a substance dissolves it goes into solution Example salt in water

Compounds can be broken down by physical means Carbonic acid in pop gives it fizz When the bottle is opened the acid breaks down into carbon dioxide and water Carbon dioxide escapes as bubbles

Mixtures can be physically separated By Density Solubility Magnetism Lab Activity Design an experiment to separate the mixture in your sample—list the steps you will take below Be sure to clean up your area when you are through 141

Test for the presence of CO2 and H2 A flaming splint is used to detect the presence of carbon dioxide or hydrogen gas CO2 extinguishes the flame H2 Creates a hydrogen burp 142