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General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1 Chapter 3 Atoms and Elements 3.1 Elements and Symbols

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Page 1: Chapter 3  lecture presentation

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

1

Chapter 3 Atoms and Elements

3.1

Elements and Symbols

Page 2: Chapter 3  lecture presentation

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

2

Elements are

pure substances that cannot be separated into simpler substances by ordinary laboratory processes

the building blocks of matter

gold carbon aluminum

Elements

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Sources of Some Element Names

Some elements are

named for planets,

mythological figures,

minerals, colors,

scientists, and places.

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A symbol

represents the name of an element

consists of 1 or 2 letters

starts with a capital letter

Examples:

1-Letter Symbols 2-Letter Symbols

C carbon Co cobalt

N nitrogen Ca calcium

F fluorine Al aluminum

O oxygen Mg magnesium

Symbols of Elements

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Some symbols are derived from Latin names, as shown

below.

Cu, copper (cuprum) Au, gold (aurum)

Fe, iron (ferrum) Ag, silver (argentum)

Symbols from Latin Names

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Physical Properties of Elements

The physical properties of an element

are observed or measured without changing its

identity

include the following:

shape

color

odor

taste

density

melting point

boiling point

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Physical Properties of Elements

Some physical properties of

copper are:

Color Red-orange

Luster Very shiny

Melting point 1083 °C

Boiling point 2567 °C

Conduction

of electricity Excellent

Conduction

of heat Excellent

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Select the correct symbol for each of the following:

A. Calcium

1) C 2) Ca 3) CA

B. Sulfur

1) S 2) Sl 3) Su

C. Iron

1) Ir 2) FE 3) Fe

Learning Check

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Select the correct symbol for each of the following:

A. Calcium

2) Ca

B. Sulfur

1) S

C. Iron

3) Fe

Solution

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Select the correct name for each symbol.

A. N

1) neon 2) nitrogen 3) nickel

B. P

1) potassium 2) phlogiston 3) phosphorus

C. Ag

1) silver 2) agean 3) gold

Learning Check

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Select the correct name for each symbol.

A. N

2) nitrogen

B. P

3) phosphorus

C. Ag

1) silver

Solution

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Chapter 3 Atoms and Elements

3.2

The Periodic Table

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Groups and Periods

On the periodic table

Groups contain elements with similar properties and

are arranged in vertical columns.

Periods are the horizontal rows of elements.

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Groups and Periods (continued)

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Periodic Table

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Group Numbers

Group Numbers

Use numbers 1–18 to identify the columns from left to

right.

Use the letter A for the representative elements (1A to

8A) and the letter B for the transition elements.

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Representative Elements

Several groups of representative elements are

known by common names.

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Alkali Metals

Group 1A(1), the alkali metals, includes lithium,

sodium, and potassium.

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Halogens

Group 7A(17),

the halogens,

includes

chlorine,

bromine, and

iodine.

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Identify the element described by the following:

A. Group 7A(17), Period 4

1) Br 2) Cl 3) Mn

B. Group 2A(2), Period 3

1) beryllium 2) magnesium 3) boron

C. Group 5A(15), Period 2

1) phosphorus 2) arsenic 3) nitrogen

Learning Check

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A. Group 7A (17), Period 4

1) Br

B. Group 2A (2), Period 3

2) magnesium

C. Group 5A(15), Period 2

3) nitrogen

Solution

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Metals, Nonmetals, and Metalloids

The heavy zigzag line

separates metals and

nonmetals.

Metals are located to

the left.

Nonmetals are located

to the right.

Metalloids are located

along the heavy zigzag

line between the metals

and nonmetals.

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Metals

are shiny and ductile

are good conductors of heat and electricity

Nonmetals

are dull, brittle, and poor conductors of heat and

electricity

are good insulators

Metalloids

are better conductors than nonmetals, but not as

good as metals

are used as semiconductors and insulators

Properties of Metals, Nonmetals,

and Metalloids

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Comparing a Metal, Metalloid,

and Nonmetal

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Identify each of the following elements as 1) metal,

2) nonmetal, or 3) metalloid.

A. sodium ____

B. chlorine ____

C. silicon ____

D. iron ____

E. carbon ____

Learning Check

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Identify each of the following elements as 1) metal, 2)

nonmetal, or 3) metalloid.

A. sodium 1 metal

B. chlorine 2 nonmetal

C. silicon 3 metalloid

D. iron 1 metal

E. carbon 2 nonmetal

Solution

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Match the elements to the description.

A. Metals in Group 4A(14)

1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn

B. Nonmetals in Group 5A(15)

1) As, Sb, Bi 2) N, P 3) N, P, As, Sb

C. Metalloids in Group 4A(14)

1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb

Learning Check

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Match the elements to the description.

A. Metals in Group 4A (14)

1) Sn, Pb

B. Nonmetals in Group 5A(15)

2) N, P

C. Metalloids in Group 4A(14)

2) Si, Ge

Solution

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Chapter 3 Atoms and Elements

3.3

The Atom

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Dalton’s Atomic Theory

Atoms

are tiny particles of matter

of an element are similar to

each other but are different

from atoms of other

elements

of two or more different

elements combine to form

compounds

are rearranged to form new

combinations in a chemical

reaction

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Subatomic Particles

Atoms contain subatomic particles.

Protons have a positive (+) charge.

Electrons have a negative (–) charge.

Like charges repel, and unlike

charges attract.

Neutrons are neutral.

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Rutherford’s Gold-Foil Experiment

In Rutherford’s gold-foil experiment, positively

charged particles

were aimed at atoms of gold

mostly went straight through the atoms

were deflected only occasionally

Conclusion:

There must be a small, dense, positively charged

nucleus in the atom that deflects positive particles

that come close.

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Rutherford’s Gold-Foil Experiment

(continued)

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Structure of the Atom

An atom consists

of a nucleus that

contains protons

and neutrons

of electrons in a

large, empty

space around the

nucleus

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Atomic Mass Scale

On the atomic mass scale for subatomic particles:

1 atomic mass unit (amu) is defined as 1/12 of the

mass of the carbon-12 atom.

A proton has a mass of about 1 (1.007) amu.

A neutron has a mass of about 1 (1.008) amu.

An electron has a very small mass, 0.000549 amu.

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Particles in the Atom

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Learning Check

Identify each statement as describing a(n) 1) proton,

2) neutron, or 3) electron.

A. __ found outside the nucleus

B. __ has a positive charge

C. __ is neutral

D. __ found in the nucleus

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Solution

Identify each statement as describing a(n) 1) proton,

2) neutron, or 3) electron.

A. 3 found outside the nucleus

B. 1 has a positive charge

C. 2 is neutral

D. 1, 2 found in the nucleus

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Chapter 3 Atoms and Elements

3.4

Atomic Number and Mass Number

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The atomic number

is specific for each element

is the same for all atoms of an element

is equal to the number of protons in an atom

appears above the symbol of an element

Atomic Number

11

Na

Atomic Number

Symbol

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Examples of atomic number and number of protons:

Hydrogen has atomic number 1; every H atom has

one proton.

Carbon has atomic number 6; every C atom has six

protons.

Copper has atomic number 29; every Cu atom has

29 protons.

Gold has atomic number 79; every Au atom has 79

protons.

Atomic Number and Protons

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State the number of protons in each.

A. A nitrogen atom

1) 5 protons 2) 7 protons 3) 14 protons

B. A sulfur atom

1) 32 protons 2) 16 protons 3) 6 protons

C. A barium atom

1) 137 protons 2) 81 protons 3) 56 protons

Learning Check

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43

State the number of protons in each.

A. A nitrogen atom

2) atomic number 7; 7 protons

B. A sulfur atom

2) atomic number 16; 16 protons

C. A barium atom,

3) atomic number 56; 56 protons

Solution

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An atom

of an element is electrically neutral; the net charge

of an atom is zero

has an equal number of protons and electrons.

number of protons = number of electrons

of aluminum has 13 protons and 13 electrons; the

net charge is zero

13 protons (13+) + 13 electrons (13–) = 0

Number of Electrons in an Atom

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Mass Number

The mass number

represents the number of particles in the nucleus.

is equal to the

number of protons + number of neutrons

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Atomic Models

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An atom of zinc has a mass number of 65.

A. How many protons are in this zinc atom?

1) 30 2) 35 3) 65

B. How many neutrons are in the zinc atom?

1) 30 2) 35 3) 65

C. What is the mass number of a zinc atom that has

37 neutrons?

1) 37 2) 65 3) 67

Learning Check

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An atom of zinc has a mass number of 65.

A. How many protons are in this zinc atom?

1) 30 (atomic number 30)

B. How many neutrons are in the zinc atom?

2) 35 (65 – 30 = 35)

C. What is the mass number of a zinc atom that has 37 neutrons?

3) 67 (30 + 37 = 67)

Solution

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An atom has 14 protons and 20 neutrons.

A. Its atomic number is

1) 14 2) 20 3) 34

B. Its atomic number is

1) 14 2) 20 3) 34

C. The element is

1) Si 2) Ca 3) Se

Learning Check

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Chapter 3 Atoms and Elements

3.5 Isotopes and Atomic Mass

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Isotopes

are atoms of the same element that have different

mass numbers

have the same number of protons but different

numbers of neutrons

Isotopes

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A nuclear symbol

represents a particular atom of an element

gives the mass number in the upper left corner and

the atomic number in the lower left corner

Example: An atom of sodium with atomic number

11 and a mass number 23 has the following atomic

symbol:

mass number

atomic number

Nuclear Symbol

23 11 Na

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For an atom, the nuclear symbol gives the number of

protons (p+)

neutrons (n)

electrons (e–)

8 p+ 15 p+ 30 p+

8 n 16 n 35 n

8 e– 15 e– 30 e–

Nuclear Symbols

16 8 O 31

15 P 65 30

Zn

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54

Naturally occurring carbon consists of three isotopes,

C-12, C-13, and C-14. State the number of protons,

neutrons, and electrons in each of the following.

protons ______ ______ ______

neutrons ______ ______ ______

electrons ______ ______ ______

Learning Check

12 6 C

13 6 C

14 6 C

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protons 6 p+ 6 p+ 6 p+

neutrons 6 n 7 n 8 n

electrons 6 e– 6 e– 6 e–

Solution

12 6 C

13 6 C

14 6 C

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Write the nuclear symbols for atoms with the

following subatomic particles:

A. 8p+, 8n, 8e– ___________

B. 17p+, 20n, 17e– ___________

C. 47p+, 60n, 47e– ___________

Learning Check

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A. 8p+, 8n, 8e–

B. 17p+, 20n, 17e–

C. 47p+, 60n, 47e–

Solution

16 8 O

37

17 Cl

107

47 Ag

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Learning Check

1. Which of the following pairs are isotopes of the

same element?

2. In which of the following pairs do both atoms have

8 neutrons?

A.

B.

C.

12 6 X 15

7 X

12 6 Z 14

6 Z

15 7 Z 16

8 Z

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Solution

1. B

Both nuclear symbols represent isotopes of carbon

with six protons each, but one has 6 neutrons and

the other has 8.

2. C

An atom of nitrogen (atomic number 7) and an atom

of oxygen (atomic number 8) each have 8 neutrons.

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Isotopes of Magnesium

In naturally occurring magnesium, there are 3 isotopes.

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Isotopes of Sulfur

A sample of naturally

occurring sulfur contains

several isotopes with the

following abundances:

Isotope % Abundance

95.02

0.75

4.21

0.02

32

16 S

33

16 S

34 16 S 36 16 S

32 33 34 36

16 16 16 16 S S S S

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Atomic Mass

The atomic mass of an element

is listed below the symbol of each

element on the periodic table

gives the mass of an “average” atom of

each element compared to C-12

is not the same as the mass number

Na

22.99

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Some Elements and Their Atomic

Mass

Most elements have two or more isotopes that

contribute to the atomic mass of that element.

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Atomic Mass for Cl

The atomic mass of chlorine is

based on all naturally

occurring Cl isotopes

not a whole number

the weighted average

of the Cl-35 and Cl-37

isotopes

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Atomic Mass for Mg

The atomic mass of Mg is

based on all naturally

occurring Mg isotopes

not a whole number

the weighted average

of the Mg-24, Mg-25, and

Mg-26 isotopes

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Using the periodic table, give the atomic mass of

each element.

A. calcium __________

B. aluminum __________

C. lead __________

D. barium __________

E. iron __________

Learning Check

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Using the periodic table, give the atomic mass of

each element.

A. calcium 40.08 amu

B. aluminum 26.98 amu

C. lead 207.2 amu

D. barium 137.3 amu

E. iron 55.85 amu

Solution

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An atom has 14 protons and 20 neutrons.

A. Its atomic number is

1) 14

B. Its atomic number is

3) 34 (14 + 20 = 34)

C. The element is

1) Si (atomic number 14)

Solution

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Chapter 3 Atoms and Elements

3.6

Electron Energy Levels

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Electromagnetic Radiation

Electromagnetic radiation

is energy that travels as waves through space

is described in terms of wavelength and

frequency

moves at the speed of light in a vacuum

speed of light = 3.0 x 108 m/s

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Electromagnetic Spectrum

The electromagnetic spectrum

arranges forms of energy from lowest to highest

arranges energy from longest to shortest wavelengths

shows visible light with wavelengths from 700–400 nm

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Learning Check

1. Which of the following has the shortest wavelength?

A. microwaves B. blue light C. UV light

2. Which of the following has the lowest energy?

A. red light B. blue light C. green light

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Solution

1. Which of the following has the shortest wavelength?

C. UV light

2. Which of the following has the lowest energy?

A. red light

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Spectra

White light that passes

through a prism

is separated into all

colors that together are

called a continuous

spectrum

gives the colors of a

rainbow

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Atomic Spectrum

An atomic spectrum consists of

lines of different colors formed when light from a

heated element passes through a prism

photons emitted when electrons drop to lower

energy levels

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Example of Atomic Spectra

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Electron Energy Levels

Electrons are arranged in

specific energy levels that

are labeled n = 1, n = 2,

n = 3, and so on

increase in energy as n

increases

have the electrons with the

lowest energy in the first

energy level (n = 1) closest

to the nucleus

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Energy Level Changes

An electron absorbs

energy to “jump” to a

higher energy level.

When an electron falls to

a lower energy level,

energy is emitted.

In the visible range, the

emitted energy appears

as a color.

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In each of the following energy level changes, indicate

if energy is 1) absorbed, 2) emitted, or 3) not changed.

A. An electron moves from the first energy level (n = 1)

to the third energy level (n = 3).

B. An electron falls from the third energy level to the

second energy level.

C. An electron moves within the third energy level.

Learning Check

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In each of the following energy level changes, indicate

if energy is 1) absorbed, 2) emitted, or 3) not changed.

A. An electron in an atom moves from the first energy

level (n = 1) to the third energy level (n = 3).

1) absorbed

B. An electron falls from the third energy level to the

second energy level.

2) emitted

C. An electron moves within the third energy level.

3) not changed

Solution

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Sublevels

Sublevels

contain electrons with the same energy

are found within each energy level.

are designated by the letters s, p, d, and f

The number of sublevels is equal to the value of the

principal quantum number (n).

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Number of Sublevels

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Energy of Sublevels

In any energy level

the s sublevel has the lowest energy

the s sublevel is followed by the p, d, and f sublevels

(in order of increasing energy)

higher sublevels are possible, but only s, p, d, and f

sublevels are needed to hold the electrons in the

atoms known today

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Orbitals

An orbital

is a three-dimensional space

around a nucleus where an

electron is most likely to be found

has a shape that represents

electron density (not a path the

electron follows)

can hold up to 2 electrons

contains two electrons that must

spin in opposite

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s Orbitals

An s orbital

has a spherical shape

around the nucleus

increases in size around the

nucleus as the energy level

n value increases

is a single orbital found in

each s sublevel

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p Orbitals

A p orbital

has a two-lobed shape

is one of three p orbitals that make up each p

sublevel

increases in size as the value of n increases

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Sublevels and Orbitals

Each sublevel consists of a specific number of

orbitals.

An s sublevel contains one s orbital.

A p sublevel contains three p orbitals.

A d sublevel contains five d orbitals.

An f sublevel contains seven f orbitals.

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Electrons in Each Sublevel

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Learning Check

Indicate the number and type of orbitals in each of the

following:

A. 4s sublevel

B. 3d sublevel

C. n = 3

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Solution

A. 4s sublevel

one 4s orbital

B. 3d sublevel

five 3d orbitals

C. n = 3

one 3s orbital, three 3p orbitals,

and five 3d orbitals

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Learning Check

The number of

A. electrons that can occupy a p orbital is

1) 1 2) 2 3) 3

B. p orbitals in the 2p sublevel is

1) 1 2) 2 3) 3

C. d orbitals in the n = 4 energy level is

1) 1 2) 3 3) 5

D. electrons that can occupy the 4f sublevel is

1) 2 2) 6 3) 14

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Solution

The number of

A. electrons that can occupy a p orbital is

2) 2

B. p orbitals in the 2p sublevel is

3) 3

C. d orbitals in the n = 4 energy level is

3) 5

D. electrons that can occupy the 4f sublevel is

3) 14

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Chapter 3 Atoms and Elements

3.7

Electron Configurations

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Energy levels are filled with electrons

in order of increasing energy

beginning with quantum number n = 1

beginning with s followed by p, d, and f

Order of Filling

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Energy Diagram for Sublevels

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An orbital diagram shows

orbitals as boxes in each sublevel

electrons in orbitals as vertical arrows

electrons in the same orbital with opposite spins (up

and down vertical arrows)

Example:

Orbital diagram for Li

1s2 2s1 2p

filled half-filled empty

Orbital Diagrams

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Order of Filling

Electrons in an atom

fill orbitals in sublevels of the same type with

one electron each until all sublevels are half full

then pair up in the orbitals using opposite spins

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Writing Orbital Diagrams

The orbital diagram

for carbon consists of

two electrons in the 1s

orbital

two electrons in the 2s

orbital

one electron each in

two of the 2p orbitals

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99

Write the orbital diagrams for

A. nitrogen

B. oxygen

C. magnesium

Learning Check

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100

Write the orbital diagrams for

A. nitrogen

1s 2s 2p

B. oxygen

1s 2s 2p

C. magnesium

1s 2s 2p 3s

Solution

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An electron configuration

lists the sublevels filling with electrons in order of

increasing energy

uses superscripts to show the number of electrons

in each sublevel

for neon is as follows:

number of electrons

sublevel 1s22s22p6

Electron Configuration

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Period 1 Configurations

In Period 1, the first two electrons enter the 1s orbital

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Abbreviated Configurations

An abbreviated configuration shows

the symbol of the noble gas in brackets that

represents completed sublevels

the remaining electrons in order of their sublevels

Example: Chlorine has a configuration of

1s22s22p63s23p5

[Ne]

The abbreviated configuration for chlorine is

[Ne]3s23p5

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Period 2 Configurations

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Period 3 Configurations

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A. The correct electron configuration for nitrogen is

1) 1s22p5 2) 1s22s22p6 3) 1s22s22p3

B. The correct electron configuration for oxygen is

1) 1s22p6 2) 1s22s22p4 3) 1s22s22p6

C. The correct electron configuration for calcium is

1) 1s22s22p63s23p63d2

2) 1s22s22p63s23p64s2

3) 1s22s22p63s23p8

Learning Check

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A. The correct electron configuration for nitrogen is

3) 1s22s22p3

B. The correct electron configuration for oxygen is

2) 1s22s22p4

C. The correct electron configuration for calcium is

2) 1s22s22p63s23p6s2

Solution

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Write the electron configuration and abbreviated

configuration for each of the following elements:

A. Cl

B. S

C. K

Learning Check

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A. Cl

1s22s22p63s23p5 [Ne]3s23p5

B. S

1s22s22p63s23p4 [Ne]3s23p4

C. K

1s22s22p63s23p64s1 [Ar]4s1

Solution

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Sublevel Blocks on the

Periodic Table

The periodic table consists of sublevel blocks

arranged in order of increasing energy.

Groups 1A(1) to 2A(2) = s level

Groups 3A(13) to 8A(18) = p level

Groups 3B(3) to 2B(12) = d level

Lanthanides/Actinides = f level

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Sublevel Blocks

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Using Sublevel Blocks

To write a configuration

using sublevel blocks

Locate the element on

the periodic table.

Starting with H in 1s,

write each sublevel

block in order going

left to right across

each period.

Write electrons for

each block.

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113

Using the periodic table, write the electron configuration

for silicon.

Solution:

Period 1 1s block 1s2

Period 2 2s → 2p blocks 2s2 2p6

Period 3 3s → 3p blocks 3s23p2 (at Si)

Writing all the sublevel blocks in order gives:

1s22s22p63s23p2

Writing Electron Configurations

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The 4s orbital has a lower energy than the 3d

orbitals.

In potassium (K), the last electron enters the 4s

orbital instead of the 3d (as shown below).

1s 2s 2p 3s 3p 3d 4s

Ar 1s2 2s22p6 3s23p6

K 1s2 2s22p6 3s23p6 4s1

Ca 1s2 2s22p6 3s23p6 4s2

Sc 1s2 2s22p6 3s23p6 3d1 4s2

Ti 1s2 2s22p6 3s23p6 3d2 4s2

Electron Configurations of the d

Level

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115

Using the periodic table, write the electron configuration

for manganese.

Solution:

Period 1 1s block 1s2

Period 2 2s → 2p blocks 2s2 2p6

Period 3 3s → 3p blocks 3s2 3p6

Period 4 4s → 3d blocks 4s2 3d5 (at Mn)

Writing all the sublevel blocks in order gives:

1s22s22p63s23p64s23d5

Writing Electron Configurations

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4s Block

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3d Block

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4p Block

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A. The last two sublevel blocks in the electron

configuration for Co are

1) 3p64s2

2) 4s24d7

3) 4s23d7

B. The last three sublevel blocks in the electron

configuration for Sn are

1) 5s25p24d10

2) 5s24d105p2

3) 5s25d105p2

Learning Check

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A. The last two sublevel blocks in the electron

configuration for Co are

3) 4s23d7

B. The last three sublevel blocks in the electron

configuration for Sn are

2) 5s24d105p2

Solution

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121

Using the periodic table, write the electron

configuration and abbreviated configuration for

each of the following elements:

A. Zn

B. Sr

C. I

Learning Check

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A. Zn

1s22s22p63s23p64s23d10

[Ar]4s23d10

B. Sr

1s22s22p63s23p64s23d104p65s2

[Kr]5s2

C. I

1s22s22p63s23p64s23d104p65s24d105p5

[Kr]5s24d105p5

Solution

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Learning Check

Give the symbol of the element that has

A. the abbreviated configuration [Ar]4s23d6

B. four 3p electrons

C. two electrons in the 4d sublevel

D. the electron configuration

1s22s22p63s23p64s23d2

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Solution

Give the symbol of the element that has

A. the abbreviated configuration [Ar]4s23d6 Fe

B. four 3p electrons S

C. two electrons in the 4d sublevel Zr

D. the electron configuration Ti

1s22s22p63s23p64s23d2

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125

Chapter 3 Atoms and Elements

3.8

Periodic Trends

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Valence Electrons

The valence electrons

determine the chemical properties of the elements

are the electrons in the outermost, highest energy

level

are related to the Group number of the element

Example: Phosphorus has 5 valence electrons.

5 valence

electrons

P Group 5A(15) 1s22s22p63s23p3

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All the elements in a group have the same number of

valence electrons.

Example: Elements in Group 2A(2) have two (2)

valence electrons.

Be 1s22s2

Mg 1s22s22p63s2

Ca [Ar]4s2

Sr [Kr]5s2

Groups and Valence Electrons

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Periodic Table and

Valence Electrons

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129

State the number of valence electrons for each.

A. O

1) 4 2) 6 3) 8

B. Al

1) 13 2) 3 3) 1

C. Cl

1) 2 2) 5 3) 7

Learning Check

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130

State the number of valence electrons for each.

A. O

2) 6

B. Al

2) 3

C. Cl

3) 7

Solution

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131

State the number of valence electrons for each.

A. Calcium

1) 1 2) 2 3) 3

B. Group 6A (16)

1) 2 2) 4 3) 6

C. Tin

1) 2 2) 4 3) 14

Learning Check

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132

State the number of valence electrons for each.

A. Calcium

2) 2

B. Group 6A (16)

3) 6

C. Tin

2) 4

Solution

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133

State the number of valence electrons for each.

A. 1s22s22p63s23p1

B. 1s22s22p63s2

C. 1s22s22p5

Learning Check

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134

State the number of valence electrons for each.

A. 1s22s22p63s23p1 3

B. 1s22s22p63s2 2

C. 1s22s22p5 7

Solution

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135

Electron-Dot Symbols

An electron-dot symbol

indicates valence electrons

as dots around the symbol of

the element

of Mg shows two valence

electrons as single dots on the

sides of the symbol Mg

· · · Mg · or Mg · or · Mg or · Mg

·

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Writing Electron-Dot Symbols

The electron-dot symbols for

Groups 1A(1) to 4A(14) use single dots · · Na · · Mg · · Al · · C ·

· Groups 5A(15) to 7A(17) use pairs and single dots. · · · · · P · : O · · ·

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Groups and Electron-Dot Symbols

in a group, all the electron-dot symbols have the

same number of valence electrons (dots).

Example: Atoms of elements in Group 2A(2) each

have 2 valence electrons.

2A(2)

· Be ·

· Mg ·

· Ca ·

· Sr ·

· Ba ·

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A. X is the electron-dot symbol for 1) Na 2) K 3) Al

B. X is the electron-dot symbol for

Learning Check

1) B 2) N 3) P

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Solution

A. X is the electron-dot symbol for 1) Na 2) K

B. X is the electron-dot symbol for

2) N 3) P

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Atomic Size

Atomic size

is described using the atomic radius

is the distance from the nucleus to the valence

electrons

increases going down a group

decreases going across a period from left to right

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Atomic Size (continued)

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Atomic Radius Within A Group

Atomic radius

increases going

down a group

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Learning Check

Select the element in each pair with the larger atomic

radius.

A. Li or K

B. K or Br

C. P or Cl

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Solution

Select the element in each pair with the larger atomic

radius.

A. K is larger than Li

B. K is larger than Br

C. P is larger than Cl

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Ionization Energy

Ionization energy

is the energy it takes to remove a valence electron

from an atom in the gaseous state

Na(g) + Energy (ionization) Na+(g) + e–

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Ionization Energy and Valence

Electrons

Ionization energy

decreases going down

a group as the distance

between the nucleus

and valance electrons

increases

146

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Ionization Energy

The ionization

energies of

metals are

low

nonmetals

are high

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Learning Check

Select the element in each pair with the higher

ionization energy.

A. Li or K

B. K or Br

C. P or Cl

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Solution

Select the element in each pair with the higher

ionization energy.

A. Li is higher than K

B. Br is higher than K

C. Cl is higher than P