Atoms and the Periodic Table

Physical Science Chapter 4

Section 1: Atomic Structure Objectives

• Explain Dalton’s atomic theory, and describe why it was more successful than Democritus’s theory.

• State the charge, mass, and location of each part of an atom according to the modern model of the atom.

• Compare and contrast Bohr’s model with the modern model of the atom.

What is an atom?

An atom is the smallest unit of an element that maintains the properties of that element.

The word atom is derived from the Greek word meaning “unable to be divided.”

Atoms are all around us… in the air you are breathing, in our chairs, even in our food!

How were atoms discovered?

In the fourth century BC, a Greek philosopher, Democritus, suggested that the universe was made of invisible units called atoms.

He thought that the movement of atoms caused the changes in matter that he observed.

Democritus tried and tried to prove his theory but was unable to provide evidence needed to convince people that atoms even existed!

How were atoms discovered?

John Dalton developed his own atomic theory in 1808.

Dalton’s Atomic Theory:• Stated that atoms could not be divided into

smaller parts• Stated that all atoms of a given element were

exactly alike• Stated that different elements could join

together to form compounds

Dalton’s Theory is considered the foundation for the modern atomic theory.

Parts of an Atom• Nucleus: small, dense center of an atom that

has a positive electric charge

• Made of protons (positive charge) and neutrons (neutral charge)

• Protons and neutrons are almost identical in size and in mass

• Electrons move around outside of the nucleus in energy levels and orbitals. • Electrons have a negative charge and are smaller

than protons or neutrons• Electrons are constantly on the move but do remain

in predictable energy levels

Atoms and their Charges

• Atoms have an overall neutral charge

• Atoms are made of an equal number of protons (positive charge) and electrons (negative charge)

• The number of neutrons (neutral charge) can change and not effect the overall charge on the atom

Models of the Atom

• In 1913, Niels Bohr suggested that electrons in an atom move in set paths around the nucleus

• The electron’s path determines the electron’s energy level• Electrons can only move in certain energy

levels. They must gain or lose energy to move from one energy level to another.

Bohr Model of a Lithium Atom

Bohr Model v. Modern Model

• In 1925, Bohr’s Model of the atom no longer explained electron behavior.

• In the Bohr Model, electrons travel around the nucleus the way that planets orbit the sun in our solar system.

• In the modern model of the atom, electrons are believed to behave more like waves on a vibrating string.

Electron Energy Levels• Within the atom, electrons with

different amounts of energy exist in different energy levels.

•The number of filled energy levels depends on the number of electrons in the atom•First Energy Level: Holds 2 Electrons•Second Energy Level: Holds 8 Electrons•Third Energy Level: Holds 18 Electrons•Fourth Energy Level: Holds 32 Electrons

Electron Orbitals• Electron Orbitals: the regions in an

atom where electrons are likely to be found

• Four different kinds of orbitals:• s-orbital• p-orbital• d-orbital• f-orbital

Valence Electrons• Valence Electrons: electrons that

are found in the outermost energy level

• Valence electrons are involved in chemical bonding

• Every atom has between one and eight valence electrons

• Noble gases have eight valence electrons and, therefore, are stable

Let’s Practice “Drawing Atoms”Let’s Practice

“Drawing Atoms”

H

He

O

Cl

N

Na

Section 2 Objectives: A Guided Tour of the Periodic Table

• Relate the organization of the periodic table to the arrangement of electrons within an atom.

• Explain why some atoms gain or lose electrons to form ions.

• Determine how many protons, neutrons, and electrons an atom has, given its’ symbol, atomic number, and mass number

• Describe how the abundance of isotopes affects an element’s average atomic mass.

Organization of the Periodic Table

• The periodic table groups similar elements together

•Makes it easier to predict the properties of an element based on placement

•The order is based on the number of protons an atom of the element has in its’ nucleus

•The periodic law states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements

Periodic Table Arrangement

• Horizontal rows in the periodic table are called periods.

•The number of protons and the number of electrons increase as you move left-to-right across a period.

•You can determine how the atom’s electrons are arranged as you move across a period.

Periodic Table Arrangement

• Vertical columns in the periodic table are called groups.

•Atoms of the same group have the same number of valence (outermost) electrons and react in a similar way.

•Atoms of the same group also have similar chemical properties.

Forming Ions• An ion is an atom or a group of

atoms that have a net electrical charge.

• Neutral atoms form ions by gaining or losing electrons.

• By using the groups in the periodic table, you can predict whether an atom will gain or lose an electron!

Example: Li atom• Lithium is found in Group 1.

•This means that there is ONE valence electron in the outer shell.

Li loses one electron

Lithium Atom:

One valence electron

Lithium Ion:

More positive now that

electron is lost

Li Li+

Example: F atom• Fluorine is found in Group 17.

•This means that there are SEVEN valence electrons in the outer shell.

F gains one electron

Fluorine Atom:

Seven valence electrons

Fluoride Ion:

More negative now that

electron is gained

F-

F

Periodic Table InformationAtomic Number

Atomic Mass Number

Element Name

Element Symbol

Atomic Number: How many protons are in the nucleus of the atom

Atomic Mass Number: How many protons and neutrons are in the nucleus of the atom

Let’s Do Some Math!

• How many protonsdoes the atom have?

• How many electrons does the atom have?

• How many neutrons does the atom have?

Ca

20

40.078

Parts of the Nucleus

Isotopes & Avg. Atomic Mass

• An isotope is an atom that has the same number of protons as other atoms of the same element but have a different number of neutrons.

• The average atomic mass for an element is a weighted average that includes all the element’s isotopes.•Average atomic mass = amu (units)

Isotopes of Chlorine

The AtomConcept

Map

Section 3 Objectives: Families of Elements

• Locate alkali metals, alkaline-earth metals, and transition metals in the periodic table.

• Locate semiconductors, halogens, and noble gases in the periodic table.

• Relate an element’s chemical properties to the electron arrangement of its atoms.

Elements: 3 Basic Groups• Metals:

•Shiny solids that can be stretched and shaped

•Good conductors of heat & electricity

• Nonmetals:•May be solids, liquids, or gases•Dull and brittle•Poor conductors of heat & electricity

• Semiconductors or Metalloids:•Under certain conditions, some

nonmetals can conduct heat & electricity

Elements: 3 Basic Groups

Metal-Type Classification• Alkali Metals: Group 1

•Reacts easily because of ONE valence electron

•Usually not found in nature alone because of reactivity—found in compounds

•Examples: •Na•K•Li

Sodium

Potassium

Lithium

Metal-Type Classification• Alkaline-Earth Metals: Group 2

•Have TWO valence electrons•Less reactive than alkali metals•Form important compounds in living

things•Shells and bone (calcium compounds)•Enzymes (magnesium compounds)

•Examples:•Mg•Ca•Ba

MagnesiumCalcium

Barium

Metal-Type Classification• Transition Metals: Groups 3-12

•Have different numbers of valence electrons

•Can form both cations and anions•Cations: positively charged ions (lose e-)•Anions: negatively charged ions (gain e-)

•Properties of transition metals change across a period

•Examples:•Au•Ag•Hg Mercury

Gold

Silver

Nonmetals

• Found on the right side of the periodic table (includes H)

• Generally have 4 or more valence electrons• Form anions easily (gain e-)

• Nonmetal compounds are plentiful on earth

• Carbon is a common nonmetal and is found in all living things

Types of Nonmetals

• Halogens: Group 17•Have SEVEN valence electrons•Form –1 anions easily (gain 1 electron)

• Highly reactive elements• Examples:

•F•Cl•Br

FluorineChlorine

Bromine

Types of Nonmetals

• Noble Gases: Group 18•Have EIGHT valence electrons•Do NOT react with other elements•Also known as inert gases

• Examples:•Ne•He•Kr

Neon

Helium

Krypton

Synthetic Elements

• Synthetic elements are man-made.•Elements with atomic numbers

greater than 92 are man-made.

• Most are radioactive•Radioactive: decaying into other

elements

• Found in the last two periods at the bottom of the periodic table

Section 4 ObjectivesUsing Moles to Count Atoms

• Explain the relationship between a mole of a substance and Avogadro’s Number.

• Find the molar mass of an element by using the periodic table.

• Solve problems converting the amount of an element in moles to its mass in grams and vice versa.

Bell Ringer:

Chapter 4

Section 4

What is a mole anyway??

• It’s not really a furry creature but a way to count in chemistry!

• Just like:12 eggs = 1 dozen; One mole of a substance =

6.022 x 1023

atoms!

Avogadro’s Constant• Chemists use large amounts of

very small particles and needed a way to count them.

• Avogadro’s Constant, named after Italian scientist, Amedeo Avogadro, defines the number of atoms in ONE mole of a substance.•One mole = 6.022 x 10

23 atoms!

•A mole is abbreviated : 1 mol

Why such a weird number?

• Since carbon-12 is found in abundance on earth,• The mole is defined as the number of atoms

in 12.00 grams of carbon-12.

• There are 6.022 x 1023

atoms of carbon-12 in 12.00 grams.

• There is a relationship between atoms and grams!

Moles and Grams are Related

• The mass in grams of 1 mol of a substance is called its molar mass.

• The molar mass (g) is the same as the average atomic mass (amu) listed on the periodic table.

• We can use conversion factors to convert:•To moles from grams •To grams from moles

Gumball Example p. 132• Given : 10 gumballs has a mass of

21.4 g• Question: What is the mass of 50

gumballs?• How to solve:

Given:

50 Gumballs

X

Conversion Factor:

21.4 g

10 Gumballs

= 107 g

Arrange so that Gumballs Cancel

Practice These!1. What is the mass of exactly 150

gumballs?2. If you want 50 eggs, how many

dozens must you buy? How many extra eggs will you have leftover?

3. If a football player is tackled 1.7 ft short of the end zone, how many more yards does the team need to get a touchdown?

Moles to Mass Problem• Determine the mass in grams of

5.50 mol of iron.

Given:

5.50 mol Fe

Conversion Factor:

55.85 grams

1 mol Fe

X = 307 g Fe

Molar Mass From Periodic

Table

Mass to Moles ProblemDetermine the amount of Iron

present in 352 grams.

Given:

352 grams Fe

Conversion Factor:

1 mol Fe

55.85 grams Fe

X = 6.30 mol Fe

Molar Mass From Periodic Table

Graphic Organizer1 mol

Molar Mass

Molar Mass

1 Mol

Number

Of

Moles

Mass

in Grams

X

X

=

=

Practice Problems

• Moles to Mass•P. 133 (# 1-4); P. 134 (# 6)

• Mass to Moles•P. 134 (# 7-9)