6.1 section objectives – page 141 relate the structure of an atom to the identity of elements....

• Relate the structure of an atom to the identity of elements.

Section Objectives:

• Relate the formation of covalent and ionic chemical bonds to the stability of atoms.

Section Objectives: • Distinguish

mixtures and solutions.

• Define acids and bases and relate their importance to biological systems.

• An element is a substance that can’t be broken down into simpler chemical substances.

ElementsElements• Everything – whether it is a rock, frog, or

flower – is made of substances called elements.

• Of the naturally occurring elements on Earth, only about 25 are essential to living organisms.

• Carbon, hydrogen, oxygen, and nitrogen make up more than 96 percent of the mass of a human body.

Natural elements in living thingsNatural elements in living things

Trace elementsTrace elements

• Trace elements such as iron and copper, play a vital role in maintaining healthy cells in all organisms.

• Plants obtain trace elements by absorbing them through their roots; animals get them from the foods they eat.

Table 6.1 Some Elements That Make Up the Human Body

Element SymbolPercent By Mass in Human Body


Molybdenum

Oxygen

CarbonHydrogen

Nitrogen

Calcium

Phosphorus

Potassium

Sulfur

Sodium

Chlorine

Magnesium

Selenium

IronZinc

CopperIodine

ManganeseBoron

Chromium

Cobalt

Fluorine

OC

H

N

Ca

P

K

S

Na

Cl

Mg

65.018.5

9.5

3.3

1.5

1.0

0.4

0.3

0.2

0.2

0.1

Fe

Zn

CuI

Mn

B

Cr

Mo

Co

Se

F

trace

trace

tracetrace

trace

trace

tracetrace

trace

trace

trace

• An atom is the smallest particle of an element that has the characteristics of that element.

Atoms: The Building Blocks of ElementsAtoms: The Building Blocks of Elements

• Atoms are the basic building blocks of all matter.

• All nuclei contain positively charged particles called protons (p+).

• The center of an atom is called the nucleus (NEW klee us).

The structure of an atom

• Most contain particles that have no charge, called neutrons (n0).

The Structure of an atom

Nucleus

Electron energy levels

• The region of space surrounding the nucleus contains extremely small, negatively charged particles called electrons (e-)

• This region of space is referred to as an electron cloud.

The Periodic Table

11 atomic number (# protons)

Na chemical symbol

22.990 atomic mass (#protons and neutrons)

The Structure of an atom

• Because opposites attract, the negatively charged electrons are held in the electron cloud by the positively charged nucleus.


• Electrons exist around the nucleus in regions known as energy levels.

• The first energy level can hold only two electrons. The second level can hold a maximum of eight electrons. The third level can hold up to 18 electrons.

Nucleus8 protons (p+)8 neutrons (n0)

Oxygen atom


• Atoms contain equal numbers of electrons and protons; therefore, they have no net charge.

• Atoms of the same element always have the same number of protons but may contain

different numbers of neutrons.

Isotopes of an ElementIsotopes of an Element

• Atoms of the same element that have different numbers of neutrons are called isotopes (I suh tophs) of that element.

• A compound is a substance that is composed of atoms of two or more different elements that are chemically combined.

Compounds and BondingCompounds and Bonding

• Table salt (NaCl) is a compound composed of the elements sodium and chlorine.

• An atom (or group of atoms) that gains or loses electrons has an electrical charge and is called an ion. An ion is a charged particle made of atoms.

How ionic bonds formHow ionic bonds form

• The attractive force between two ions of opposite charge is known as an ionic bond.

Chemical ReactionsChemical Reactions

• Atoms combine with other atoms only when the resulting compound is more stable than the individual atoms.

How covalent bonds formHow covalent bonds form

• For many elements, an atom becomes stable when its outermost energy level is full.

• Sharing electrons with other atoms is one way for elements to

become stable.

• Two hydrogen atoms can combine with each other by sharing their electrons.


• Each atom becomes stable by sharing its electron with the other atom.

Hydrogen molecule


Click image to view movie.

How covalent bonds formHow covalent bonds form• The attraction of

the positively charged nuclei for the shared, negatively charged electrons holds the atoms together.

Hydrogen molecule

• A covalent bond holds the two hydrogen atoms together.


• A molecule is a group of atoms held together by covalent bonds. It has no overall charge.

Water molecule

• Chemical reactions occur when bonds are formed or broken, causing substances to recombine into different substances.

Chemical ReactionsChemical Reactions

• All of the chemical reactions that occur within an organism are referred to as that organism’s metabolism.

• In a chemical reaction, substances that undergo chemical reactions, are called reactants.

Writing chemical equationsWriting chemical equations

• Substances formed by chemical reactions, are called products.

• A molecule of table sugar can be represented by the formula: C12H22O11.

Writing chemical equationsWriting chemical equations

• The easiest way to understand chemical equations is to know that atoms are neither

created nor destroyed in chemical reactions. They are simply rearranged.

• A mixture is a combination of substances in which the individual components retain their own properties.

Mixtures and SolutionsMixtures and Solutions

• Neither component of the mixture changes.

• A solution is a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent).

Mixtures and SolutionsMixtures and Solutions

• Sugar molecules in a powdered drink mix dissolve easily in water to form a solution.

• Chemical reactions can occur only when conditions are right.

Acids and basesAcids and bases

• A reaction may depend on:- energy availability- temperature- concentration of a substance

- pH of the surrounding environment

• The pH is a measure of how acidic or basic a solution is.


• A scale with values ranging from below 0 to above 14 is used to measure pH.

More acidic Neutral More basic

• Substances with a pH below 7 are acidic. An acid is any substance that forms hydrogen ions (H+) in water.


• A solution is neutral if its pH equals seven.

More acidic Neutral More basic

• Substances with a pH above 7 are basic. A base is any

substance that forms hydroxide ions (OH-) in water.


pH 11

Question 1

Which of the following is an element?

D. water

C. sodium chloride

B. carbon

A. chlorophyll

The answer is B. An element can't be broken down into simpler chemical substances. Chemical elements combine in different ways to form a variety of substances useful to living things.

Table 6.1 Some Elements That Make Up the Human Body



Molybdenum

Oxygen

CarbonHydrogen

Nitrogen

Calcium

Phosphorus

Potassium

Sulfur

Sodium

Chlorine

Magnesium

Selenium

IronZinc

CopperIodine

ManganeseBoron

Chromium

Cobalt

Fluorine

OC

H

N

Ca

P

K

S

Na

Cl

Mg

65.018.5

9.5

3.3

1.5

1.0

0.4

0.3

0.2

0.2

0.1

Fe

Zn

CuI

Mn

B

Cr

Mo

Co

Se

F

trace

trace

tracetrace

trace

trace

tracetrace

trace

trace

trace

The smallest particle of an element that has the characteristics of that element is a(n) __________.

Question 2

D. atom

C. nucleus

B. electron

A. proton

The answer is D. Atoms are the basic building blocks of all matter and have the same general structure, including a nucleus and electrons. Elements found in both living and nonliving things are made of atoms.

Nucleus


An atom has a nucleus and electrons in energy levels.

Which of the following can contain two types of particles?

D. electrons

Question 3

B. protons

C. neutrons

A. nucleus

The answer is A. The nucleus is the center of the atom and may contain both positively charged particles and particles that have no charge.

Nucleus8 protons (p+)8 neutrons (n0)

Oxygen atom

Question 4

B. Sodium and chlorine atoms have no overall electrical charge.

A. Sodium and chlorine are sharing electrons in their outer energy levels.

Sodium and chlorine combine to form table salt. What do you know to be true?

Question 4

D. Sodium and chlorine atoms in table salt have full outer energy levels.

C. Sodium and chlorine are less stable in the compound sodium chloride.

Sodium and chlorine combine to form table salt. What do you know to be true?

The answer is D. Sodium and chlorine atoms combine because the resulting compound, table salt, is more stable than the individual atoms. Sodium loses an electron in its outer energy level, chlorine gains that electron in its outer energy level, and an ionic bond is formed.

6.1 section objectives – page 141 relate the structure of an atom to the identity of elements....

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