Unit 1: Atoms, Elements, & Compounds Section 3.1: Compounds

Compounds Q: What is a pure substance? A compound is a pure substance made up of two or more kinds of elements that are chemically combined. Q: What is a pure substance?

Chemical Bonds Formed when atoms combine together to form molecules or compounds. Two main types: Covalent Ionic

Covalent Compounds Formed from a sharing of electrons between atoms. Always formed from non-metals. Results in the formation of a molecule. The atoms in molecules are held together by shared electrons. ALL atoms end up with the FULL NUMBER of electrons. They are ALL satisfied!!! Examples: Water – H2O Glucose – C6H12O6

Covalent…….cont.. Covalent compounds (molecules) are best shown with Lewis Dot Diagrams or a Ball and Stick Model. What do you notice about the number of electrons in A? What molecule is this? What is it’s formula?

Practice Question – Draw a Lewis Dot Diagram for each of the following atoms. Place only the valence electrons. Atom C H O S Structure (Put the symbol in the middle and space the electrons evenly around the outside. If there’s more than 4, you must have pairs.

Lewis Dot Structures of Molecules Formula H2O CO2 CH4 Structure of individual Atoms Structure of Molecule

Pause for Thought What is the key idea behind Covalent Bonding? Do questions 1-3 on page 75 and 1-3 and 7 on page 79.

Ionic Compounds Ionic Compounds form when two ions are attracted to each other. Ions form when atoms loose or gain electrons to become like the nearest noble gas. Q: Which noble gas does the Na+ ion resemble? Cl-?

Ionic compounds cont… Look at this diagram again: Q: Where did sodium’s extra electron go? Q: What does this do to the sodium atom? Q: What happens to the chorine atom as a result?

Formation of Ions Ions Atoms Ion Energy Level Diagram Symbol with Charge Sodium Choride Flouride Atom Energy Level Diagram Sodium Chlorine Flourine

Ionic Compounds cont…. When a metal atom forms an ion, it becomes positively charged. When a non-metal forms an ion, it becomes negatively charged. These oppositely charged ions attract each other. When huge numbers of negative and positive ions attract each other they form an ionic lattice. Positives attract negatives, positives repel positives and negatives repel negatives.

NaCl lattice This shows how several Na+ and Cl- ions form an ionic lattice. You see it as table salt!!!! Q: How many sodium ions are there for every chloride ions?

Ionic vs. Covalent Compounds Metal and non-metal combo. Transfer of electrons. Solid at room temperature. High melting and boiling points. Not electrically conductive as solids but very conductive when dissolved in water. Are referred to as salts. E.g. CaCO3 – Calcium carbonate Non-metals only. Sharing of electrons. Do not conduct electricity. May be solids, liquids or gases at room temperature. Have many uses. E.g. Crude oil has many covalent compounds mixed together.

Pause for thought Q: What is the main idea behind ionic bonding? Do questions 4 and 5 on page 75 and 1-11 on page 79.