Chemistry Overview Physical Science Unit 6

Changes There are two types of changes Physical changes – A physical change is when the shape or state of something is altered but it remains the same substance For example: Cutting a piece of paper into pieces Freezing water Boiling water Chemical changes - A chemical change is when substances combine to form a new product this new product will have different physical and chemical properties For Example rusting of iron Burning wood (combustion) Cooking an egg explosion of fireworks rotting bananas milk going sour

Chemical Substances Every substance in the periodic table has chemical and physical properties Physical properties help us identify substances Boiling point Freezing/melting point Density Solubility Viscosity Conductivity Chemical properties predict how the substances will react Reactivity Toxicity Flammability Oxidation Stability

Chemical Bonds Elements from the periodic table bond with each other forming everything around us The elements bond in specific ways Scientists have grouped chemicals down each column based on similar bonding properties Based on their chemical properties substances will undergo chemical Changes

Ionic and Covalent Bonds Covalent bonds are usually formed when atoms of nonmetals share Ions Ionic bonds form bonds between metals (or metalloids) and nonmetals

Ionic Bonds Ions can be negative or positive Remember ELECTRONS move the other particles don’t Negative Ions are formed when an atom gains electrons from another atom Positive Ions are formed when an atom loses electrons to another atom

Ionic Bonds Since Ionic bonds involve both metals and nonmetals it’s important to know where these are on the periodic table

Ionic Bonds Equally important is figuring out which ones go together That will be based on the number of electrons on the outer shell of a substance And it’s also based on the fact that opposites attract each other

Ions There are two types of Ions Cations – have an overall positive charge Anions – have and overall negative charge Again ….. Electrons move that means Cations have given away an electron Anions have taken on an electron

Electron Shells – Ions

Electron Shells

The variable ones The transition metals can vary they will sometimes give up 1, 2, or 3 electrons depending on the substance they are reacting with

Chemical Formulas When ions combine the formula is written as: Steps in writing formulas: Use a periodic table of elements and of ions. Write the symbol and charge of the cation first (positive ion) Write the symbol and charge of the anion next (negative ion) Use criss-cross rule to balance for an electrically neutral compound. Example: CationAnionFormula 1. Sodium chlorideNa+ Cl- NaCl 2. Magnesium oxide Mg2+ O2- MgO 3. Calcium bromide Ca2+Br-CaBr 2 4. Aluminum sulphide Al3+ S2- Al 2 S 3

Conservation of Matter Conservation of matter – Matter is not created or destroyed it is changed into a different form During a chemical reaction the amount of matter stays the same Scientists have shown this by doing experiments in a closed system A closed system means nothing is allowed to escape (ie. Gases ) If you mass all the substances before a chemical reaction and then after you will find the totals will match even though you have different substances in the end

Chemical Reactions There are four types of chemical reactions synthesis A + B AB Decomposition AB A + B single replacement A + BC AB + C Double replacement AB + CD AC + BD

Chemical Equations Since “conservation of Matter” has been proven we must have a balanced chemical reaction when we look at the equation Chemical Reaction vocabulary Reactants – these are the substances on the Left side Products – these are the substances on the Right side Coefficient - this is the number in front of the chemical formula Subscript – the number inside the chemical formula that cannot be changed because it is a property of the formula superscript – the number at the top right corner of an ion, it will be positive or negative depending on the substance

Rules for Balancing Equations The subscript CANNOT be changed You always want to start with the coefficient of 2 (unless you can do this in your head) The coefficient has distributive properties just like in math 2AB means you have 2 of A and 2 of B If there is a subscript the distributive property applies to the subscript 2A 3 B means you have 6 of A and 2 of B

Steps for Balancing Equations 1. Identify what you have first H 2 + O 2 H 2 O PLEASE take your time doing this otherwise everything will be wrong2 H 2 O 1 O You can see the equation is not balanced because the amount of Oxygen is not equal on both sides

Steps for Balancing Equations 2. Begin with the side that has the lower number H 2 + O 2 H 2 O2 H 2 O 1 O This would be the right side since there is one oxygen compared to 2 oxygens H 2 + O 2 2H 2 O 2 H4 H 2 O Not balanced now we have too many hydrogens on the right

Steps for Balancing Equations 3. Change only one thing at a time H 2 + O 2 2H 2 O 2 H4 H 2 O How could you get 4 Hydrogens on the right side ? 2H 2 + O 2 2H 2 O4 H 2 O Balanced? YESSS

Naming Compounds - Ionic The names for ionic compounds are very simple. The first part of the name is simply the name of the metal element. The second part of the name is the name of the nonmetal element, with the ending changed to the suffix –ide. For example, consider the compound Al 2 O 3. The first part of the name would be aluminum. For the second part of the name, we drop the ending on oxygen and add –ide, thus it becomes oxide. The name of the compound is then aluminum oxide. When an ionic compound contains a transition metal, the names become a bit more complicated For example, iron and chlorine form two different compounds, FeCl 2 and FeCl 3. To distinguish them, we add a Roman numeral to indicate the charge on the metal ion. For FeCl 2, The name of this compound is then iron(II) chloride. For FeCl 3, The name of the compound is iron(III) chloride.

Naming Compounds - Covalent The first two steps are similar to naming ionic compounds The first part of the name is simply the name of the first element. The second part of the name is the name of the other element, with the ending changed to the suffix –ide. The third step is to determine a prefix that shows the number of atoms of that element in the molecule For example: N 2 O 3 Nitrogen Oxide (steps 1 and 2) There are 2 atoms of Nitrogen and 3 of Oxygen Looking at the prefix table ( you will have to learn it) Dinitrogen trioxide