12 Chapter 2

Write the chemical symbol for each of the following elements, and state whether it is one ofthe four elements used by living things in large amounts (L), whether it is used in moder-ate amounts (M), or whether it is a trace element (T) required in small amounts.

Amount Element Amount

A compound is a substance that contains two or more elements in a fixed ratio. Indicatewith a check mark which of the following are elements and which are compounds. (Youwill have to guess on some!)

Element Compound

l-. Table salt

2. Calcium

3. Water

4. Vitamin A

5. Carbon

6. Sultur

7. Carbon dioxide (CO2)

B. DNA

9. Iodine

10. Protein

Element

9. Phosphorus

10. Nitrogen

The Chemical Basis of Life t3

These modules introduce atoms. It is most important to know what the subatomic particlesare, where they are located in an atom, and that atoms of different elements diJfer because

they contain different numbers of protons. Some atoms not covered in these modules are

compared below. You can figure out the subatomic particles they contain based on the con-cepts in the modules. First, fill in the blanks. Then sketch each atom,labeling and coloringprotons red, neutrons gray/ and electrons blue. (Coloring will help you focus on and re-member which is which.)

Element

Carbon-12

fe)VNitrogen-L42.

1.

Symbol

714

AtomicNumber

6

MassNumber

12

Number ofProtons

6

Number ofNeutrons

6

Number ofElectrons

6

3. Chlorine-35

4. Oxygen-L6

5. Oxygen-17

1735

14 Chapter 2

Atoms of four elements important to life are diagrammed below. Pay particular attentionto their electron shells. Remember that atoms with incomplete outer electron shells partic-ipate in chemical reactions that allow them to attain complete outer shells: 2 electrons fora hydrogen atom, 8 electrons for most other elements important to life.

cHLORTNE (Cr)

Atomic number = 17

HYDROGEN (H)Atomic number = 1

@ @NITROGEN (N)Atomic number = 7

1. Given the irrformation and diagrams above, show how electrons would be trans-ferred between calcium and chlorine atoms to form calcium and chloride ions, whichwould then attract each other to form calcium chloride, CaC12. (Hinfi An atom cangain or lose more than one electron.)

2. Using the information and diagrams above, show how nitrogen could form covalentbonds with several hydrogen atoms, forming a molecule of ammonia. What wouldbe the molecular formula for ammonia?

CALCIUM (Ca)Atomic number = 20

l8 Chapter 2

Review basic chemical terrninology by completing this crossword puzzle.

Across2. _is the energy

due to movement ofmolecules in a body ofmatter.

5. Arr-is a sub-atomic particle that cir-cles an atom's nucleus.

7. The smallest parti-cle of an element iscalled an _.

9. An_isacharged atom or mole-cule.L2. Acid

- is caused

by pollutants that com-bine with water in theair.L5.

-is anything

that occupies space andhas mass.

17. Two ormore atomsheld together by cova-lentbonds form a

-.L9. Neutrons and pro-tons are found in anatom's _.22. The cohesion ofwater molecules is re-soonsible for surface23. Variant forms of an element with different numbers of neutrons are called24.

-is the tendency of water molecules to stick together.

Down1. A

- is a subatomic particle with no electrical charge.

3.

- measures the intensity of heat.

4. Electrons are shared unequaliy in a

- covalent bond.

5. There are92naturally occurring _.6. A

- contains two or more elements in a fixed ratio.

8. Weak bonds between water molecules are called

- bonds.

10. An

- donates H+ ions to solutions.

11. A

-bond is formed when two atoms share electrons.

13. A

- is a positively charged particle from the nucleus of an atom.

14. In a solution, the dissolving agent is called the

-.15. A

- is a liquid containing a uniform mixture of substances.

18. When two ions of opposite charges attract each other, an

- bond forms.

20. The

- is the substance dissolved in a solution.

21,. A- accepts H+ ions and removes them from solution.