1. Chapter 2: Chemical Bonds & Compounds
Section 1: Elements and Compounds

2. Compounds
The properties of an element are often very different than the compounds they form.
For example, sugar is made of carbon, hydrogen, and oxygen – but is very different than any of these elements alone.
Calcium = soft metallic solid; chlorine = greenish gas poisonous to human.
When they are bonded together, they form calcium chloride = nonpoisonous white solid.

3. Compounds
A compound is a substance made of atoms of two or more elements.
There are millions of compounds, held together by chemical bonds.
Compounds change based on the elements and the arrangement of elements.

4. Combining Atoms
Compounds always contain atoms of elements in a specific ratio.
For example, carbon dioxide = CO2, with one carbon atom and 2 oxygen atoms.
If we change the number of oxygen atoms to one, then we have carbon monoxide = CO, a very different compound.

5. Chemical Formulas
A chemical formula uses chemical symbols to represent the atoms of elements and their ratios in a chemical compound.
You need:
1. chemical symbol (C for Carbon, O for oxygen)
2. The amount of each atom: for one atom, do not put a number; for more than 1, put the number in subscript to the right.
CO2

6. Same Elements, Different Compounds
Even when compounds are made of the same elements, the ratios must be different, causing the substances to be different.
For example, hydrogen and oxygen can be combined in different ways.
Two hydrogen + 1 oxygen = water (H2O)
Two hydrogen + 2 oxygen = hydrogen peroxide (H2O2)

7. Practice Writing Formulas
Methane = 1 Carbon, 4 Hydrogen
Sulfuric Acid = 2 Hydrogen, 1 Sulfur, 4 Oxygen
Glucose = 6 Carbon, 12 Hydrogen, 6 Oxygen
Formic Acid = 1 Carbon, 2 Hydrogen, 2 Oxygen

8. Chapter 2: Chemical Bonds & Compounds
Section 2: Chemical bonds

9. Chemical Bonds
Chemical bonds hold atoms of elements together in compounds like glue.
They form when the electron clouds between atoms interact.

10. Transferring Electrons
Remember, ions are formed when atoms gain or lose electrons.
Gaining = negative charge; losing = positive charge.
Group 1 usually loses one electron; group 2 loses 2 electrons.
Group 16 gains two electrons; group 1 gains 1 electron.

11. Ionic Bonds Some elements work well together to form bonds.
If group 1 likes to lose electrons, and group 17 likes to gain electrons – they can give and take electrons to each other to form bonds.
If sodium (Na) wants to give an electron to Chlorine (Cl), Na+ and Cl- are formed.
The positive and negative ions are attracted to one another = ionic bond.

12. Ionic Bonds Electrical charges go out in all directions.
Each ion attracts the opposite ions surrounding it. When many ions are attracted to one another, a crystal can be formed.
The way these ions bond to one another effects the shape of the substance formed;
In sodium chloride, each positive ion has 6 negative ions around it, and each negative ion has 6 positive ions around it = forms a cube.

13. Ionic Bonds
Very stable bonds.
Form strong crystals.

14. Naming Ionic Bonds Step 1: Keep the name of the positive ion.
Step 2: Drop the last part of the negative ion’s name, and add –ide.
Step 3: put the positive ion name first, and then put the changed negative ion’s name.

15. Naming Ionic Bonds - Example
Na+Cl-
Positive Ion = Sodium
Negative Ion = Chlorine; drop –ine and add –ide.
Name = Sodium Chloride

16. Molecules
Molecule: group of atoms held together by covalent bonds; two-many thousands of atoms.
Most have more than one type of element; some are pure substances though:
H2, N2, O2, F2, Cl2, Br2, and I2

17. Polar Covalent Bonds A bond in which electrons are not shared evenly.
For example, in a water molecule, the oxygen (8 protons in nucleus) has a much stronger pull on electrons than hydrogen (1 proton in nucleus).
Because of this, the oxygen will have a slightly negative charge – more e-.

18. Ionic Compounds
Regular crystal structure that depend on the ratio and sizes of the ions in bond.
Shatter when pressure is applied

19. Covalent Compounds
Each molecule has its own shape – molecular structure.
See and copy the following example on page 54.
Linear – iodine
Bent – water
Pyramid – ammonia
Complex – methane
Effects odors, reactions, uses, etc.

20. Chapter 2: Chemical Bonds & Compounds
Section 3: Properties and Bonds