Consider the characteristics of a living and a nonliving thing



TIPS FOR MASTERING KEY CONCEPTS

Living things are composed of chemicals, and life processes follow chemical rules. All matter, living and nonliving is made up of atoms. Atoms can interact by transferring electrons and forming ions or by sharing electrons and forming molecules.

Atoms are nature's building material.

• All matter is made of atoms.

• Atoms are composed of negatively charged electrons, which orbit around a nucleus containing positively charged protons and neutral neutrons.

• Electrons have potential energy, and the further they are from the nucleus, the greater their energy.

• The number of electrons in the outermost energy level of orbits determines the chemical behavior of an atom.

• Atoms behave in ways that establish full outermost energy levels and that balance positive and negative charges.

Elements are pure substances that cannot be broken down into other substances.

• Only 11 of the 92 naturally occurring elements are present in organisms in significant amounts, and the vast majority of an organism's weight comes from just four elements (carbon, oxygen, hydrogen and nitrogen).

Compounds are formed from different combinations of elements.

• Elements in compounds occur in fixed ratios.

• Compounds cannot be broken down by physical means (e.g., tearing or crushing).

Chemical bonds hold compounds together.

• When electrons are transferred from one atom to another, ions are formed, and ionic bonds hold the oppositely charged ions together to form ionic compounds in a crystal structure.

• When pairs of electrons are shared between atoms, strong covalent bonds are formed resulting in relatively stable molecules.

Hydrogen bonds and van der Waals forces are weak attractive forces between molecules

• Hydrogen bonds occur between

• van der Waals forces are very weak.

1. Scan the headings and boldfaced words in Section 1 of the chapter and predict two things that you think might be discussed.

a.

b.

2. Use your book or dictionary to define the word substance.

3. Define the following terms:

atom

electron

neutron

nucleus

proton

4. Complete the paragraph below using the following terms:

compound covalent bond element ion ionic bond

isotope molecule van der Waals force

A substance that cannot be broken down into other substances is a(n) _____________. Carbon-14 is a(n) ________________. It has a different number of neutrons than other carbon atoms. A(n) __________________ forms when two or more elements combine. The chemical bond that holds the elements together is a(n) _________________ when electrons are shared. A substance with this kind of bond is called a(n) ____________________. An atom that has lost or gained one or more electrons becomes a(n) __________________, which carries an electric charge. Two of these oppositely charged atoms can form an electrical attraction called a(n) ____________________. An attraction between oppositely charged regions of molecules is called a(n) ___________________________.

5. Draw an oxygen atom and label the parts. Be sure to note the type of electric charge for each part.

6. The overall charge of the oxygen atom is ________, because the atom

.

7. Compare and contrast the characteristics of carbon-14 by completing the following sentences;

a. Structurally, carbon-14 differs from other carbon atoms because

b. Carbon-14 is radioactive because

8. Knowing the half-life of carbon-14 enables scientists to

9. Identify four unique characteristics of compounds.

10. Label the following parts of the water molecule illustrated below.

• hydrogen atom(s) • first energy level • oxygen atom(s)

• second energy level • covalent bonds

11. Compare positively and negatively charged ions.

12. Identify the type of substances held together by van der Waals forces. Include indicators of electric charges.

13. A chemical compound in your toothpaste helps protect your teeth from decay. The formula for this compound is Na2PO3F. Use the periodic table in your book to identify each element in this compound.

Na2

P

O3

F

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Compounds

[pic]

Atom

becomes

positively charged

when it

negatively charged

when it

van der Waals

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