SECTION 3.1Atomic Structure

ATOMS AND THE PERIODIC TABLE

Chapter Preview 3.1 Atomic Structure

What are Atoms? What’s in an Atom? Models of the Atoms

3.2 A Guided Tour of The Periodic Table Organization of the Periodic Table Some atoms form Ions How Do the Structures of Atoms Differ?

3.3 Families of Elements How Are Elements Classified?

Metals Nonmetals

3.4 Using Moles to Count Atoms Counting Things Calculating with Moles

UNDERSTANDING OF ATOMS

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

Atom meaning “unable to be divided” However, Democritus theory of atoms was

unconvincing to other scientists, which led to more research.

DALTON’S ATOMIC THEORY In 1808, an English teacher, John Dalton,

proposed his own theory: Every element is made of tiny, unique particles

called atoms that cannot be subdivided Atoms of the same element are exactly alike. Atoms of different elements can join to form

molecules. Ex. H2O

WHAT’S IN THE ATOM?

At the center of the atom there is a nucleus made of protons and neutrons.

On the outside of the nucleus are where the electrons are located.

Protons have a positive charge Electrons have a negative charge Neutrons are neutral

MODEL OF THE ATOM In 1913, the Danish scientist, Niels Bohr,

suggested that electrons in an atom move in set paths around the nucleus much like planets orbit the sun.

Each electron has a certain path known as the energy level.

However, the modern model determined that electrons did not orbit the nucleus in set paths but behaved more like waves on a vibrating string

It is impossible to determine both the exact location of an electron and its speed and direction

ORBITALS

Electrons are found in a region called an orbital

There are 4 different types of orbitals: S orbital which is the simplest and more

likely to surround the nucleus

Z

X

Y

ORBITALS

The second is the P orbitals, which are dumbell shaped and can be 3 different ways in space.

Z

X

Y Z

X

YX

Z

Y

ORBITALS The last are the d orbitals, which occur 5

ways in space and the f orbitals, which occur 7 ways in space.

Each orbital can only hold 2 electrons Electrons will occupy the lowest energy

levels first, which mean they occupy orbitals with the lowest energy.

Orbitals are occupied in this order: s – p – d – f

VALENCE ELECTRONS

Every atom has 1 or more valence electrons Valence electrons are in the outermost

energy level of an atom.

SECTION 3.1 SUMMARY Elements are made of very small units called atoms. The nucleus of an atom is made of positively charged

protons and uncharged neutrons. Surrounding the nucleus are tiny negatively charged

electrons. Atoms have an equal number of protons and

electrons. In Bohr’s model of the atom, electrons orbit the

nucleus in set paths much like the planets orbit the sun in our solar system.

In the modern atomic model, electrons are found in orbitals within each energy level.

Electrons in the outermost energy level are called valence electrons.

SECTION 3.2A GUIDED TOUR OF THE PERIODIC

TABLE

Section 3.2 Objective 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

isotope has, given its symbol, atomic number, and mass number.

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

ORGANIZATION OF PERIODIC TABLE

In a grocery store you know where everything is because of the organization. The Periodic Table is the same way!

The Periodic Table is organized in a special way. Elements are arranged by increasing number of protons.

PERIODIC LAW

States that elements are arranged in this special way because similarities in properties will occur.

Elements that are horizontal are the Period Elements that are Vertical in a column are a

Group and also have the same valence electrons.

USING THE PERIODIC TABLE TO DETERMINE ELECTRONIC

ARRANGEMENT.

Period: a horizontal row of elements in the periodic table.

Group (family): a vertical column of elements in the periodic table.

Elements in the same group have similar properties.Period

group

SOME ATOMS FORM IONS Ionization: the process of adding electrons to or

removing electrons from an atom or group of atoms. For example, ionization between sodium and chlorine.

Naming atoms that have completed the ionization process. Ion: an atom or group of atoms that has lost or gained

one or more electrons and therefore has a net electric charge.

Cation: an ion with a positive charge. For Example; Na+

Anion: an ion with a negative charge. For Example; Cl-

IONIZATION

Remember what ionization means! When ionization occurs the atom no longer

has the same number of electrons and protons and an ion is formed.

If an atom loses an electron, it forms a positive charged ion called a cation.

Ex. Lithium atom Lithium ion

Li+

IONIZATION

If an atom gains an electron it forms a negative charged ion called an anion.

Ex. Fluorine atom

F-

HOW DO THE STRUCTURES OF ATOMS DIFFER?

As you have seen with sodium and chlorine, atoms of different elements have their own unique structures.

Because these atoms have different structures, they have different properties. See below: it only took one more or one less to make gold or to make mercury.

ATOMIC NUMBER EQUALS THE NUMBER OF PROTONS.

Atomic number: the number of protons I the nucleus of an atom.

MASS NUMBER EQUALS THE TOTAL NUMBER OF SUBATOMIC PARTICLES IN

THE NUCLEUS.

ISOTOPES

Isotopes: any atoms having the same number of protons but different numbers of neutrons.

For example; Hydrogen has three isotopes all share similar chemical properties because each is made of one proton and one electron.

CALCULATING THE NUMBER OF NEUTRONS IN AN ATOM

If you know the atomic number and mass number of an atom, you can calculate the number of neutrons it has. Mass number (A) Atomic Number (Z) Number of neutrons

For Example: Uranium has an atomic number of 92 and has a mass number of 235. So, the number of neutrons must be ?

Mass number: 235 Atomic Number: 92 Number of neutrons: 143

THE MASS OF AN ATOM The mass of a single atom is very small. Atomic mass unit (amu): a quantity equal

to one-twelfth of the mass of a carbon-12 atom.

Average atomic mass: the weighted average of the masses of all naturally occurring isotopes of an element.

SECTION 3.2 SUMMARY Elements are arranged in

order of increasing atomic number so that elements with similar properties are in the same column, or group.

Elements in the same group have the same number of valence electrons.

Reactive atoms may gain or lose valence electrons to corm ions.

An atom’s atomic number is its number of protons.

An atom’s mass number is its total number of subatomic particles in the nucleus.

Isotopes of an element have different numbers of neutrons, and therefore have different masses.

An element’s average atomic mass is weighted average of the masses of its naturally occurring isotopes.

SECTION 3.3FAMILIES OF ELEMENTS

Section 3.3 Objectives 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 electron

arrangement of its atoms.

HOW ARE ELEMENTS CLASSIFIED?

Elements are classified as metals or nonmetals.

This classification groups elements that have similar physical and chemical properties.

Element Major Groups: Metals: the elements that are good conductors

of heat and electricity

Semiconductors: the elements that are intermediate conductors of heat and electricity.

Alkali Metals: the highly reactive metallic elements located in Group 1 of the periodic table.

Alkaline-earth metals: the reactive metallic elements located in Group 2 of the periodic table.

Transition metals: the metallic elements located in groups 3-12 of the periodic table

NONMETAL: EXCEPT FOR HYDROGEN, NON METALS ARE FOUND ON THE RIGHT SIDE OF THE PERIODIC TABLE.

Nonmetals: the elements that are usually poor conductors of heat and electricity.

NON METALS INCLUDE SOME ELEMENTS IN GROUPS 13-16 AND ALL THE ELEMENTS GROUPS 17-18 Carbon is found in three different forms and

can also form many compounds. Glucose Chlorophyll Isooctane

Nonmetals and their compounds are plentiful on Earth

Chlorine is a halogen that protects you from harmful bacteria

THE NOBEL GAS NEON IS INERT

Nobel (inert) gases: the unreactive gaseous elements located in Group 18 of the periodic table.

Examples of Nobel Gases:

He Ne Ar Kr Xe Rn

SECTION 3.3 SUMMARY Metals are shiny solids

that conduct heat and electricity.

Alkali metals, located in group 1 of the periodic table, are very reactive.

Alkaline-earth metals, located in Group 2, are less reactive than alkali metals.

Transition metals, located in Groups 3-12, are not very reactive.

Nonmetals usually do not conduct heat or electricity.

Nonmetals include the inert noble gases in Group 18, the reactive halogens in Group 17, and some elements in Groups 13-16.

Semiconductors are non metals that are intermediate conductors of heat and electricity.

SECTION 3.4USING MOLES TO COUNT ATOMS

Section 3.4 Objectives: Explain the relationship between a mole of a

substance and Avogadro’s constant.

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

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

COUNTING THINGS

Eggs are counted by the dozen, peaches are counted by the bushel, and paper is counted by the ream.

There are many different counting units. Feet gallons Inches quarts Miles meters

The unit used by Scientists to count atoms is the mole: Mole: the SI base unit that describes the amount

of a substance. Abbreviated mol. Note: A mole is a collection of a very large

number of particles.

A mole has 602,213,670,000,000,000,000,000 particle to be exact.

This long number is usually written as 6.022 x 10 23 / mole and is referred to as Avogadro’s constant.

So, if you have 1 mole of gumballs how many gumballs would you have?

In chemistry, the conversion factor is molar mass (the mass of one mole). This value has been calculated for each element and is usually included in a periodic table. In most periodic tables of the elements, the molar mass value is located in the top right hand corner of an element's cell.

The value 55.85 g/mol means that a mole of iron atoms 6.02 x 1023 (atoms) has a mass of 55.85 grams. In the next lesson, you will see how molar mass values can be used to convert mole amounts to mass and vice versa.

MOLE AND GRAMS ARE RELATED The mass in grams of 1 mol of a substance.

Example 1, 1 mol of carbon – 12 atoms has a molar mass of 12.00

g. In this 1 mol of carbon-12 there is 6.022 x 10 23 carbon-12 atoms / mol.

Example 2: 1 mol of Magnesium has a molar mass of 24.30 g. In

this 1 mol of Magnesium there is 6.022 x 10 23 / Magnesium atoms / mol.

Let connect how Moles to Grams are related. Note: The molar mass of an element in grams is

the same as its average atomic mass in amu. This information can be found in the periodic table.

CALCULATING WITH MOLES: Because the amount of a substance and its

mass are related, it is often useful to convert moles to grams, and vice versa. You can use conversion factors to relate units. For example; 12 eggs equal 1 dozen and 12 inches equal 1 foot.

Conversion factor: a ration equal to one that expresses the same quantity in two different ways.

Converting between the amount of an element in moles and its mass in grams is outlined below.

SECTION 3.4 SUMMARY One mole of a

substance has as many particles as there are atoms in exactly 12.

Avogadro’s constant, 6.022 x 1023 / mol, is equal to the number of particles in one mol of substance (pure).

Molar mass is the mass in grams of 1 mol of a substance.

An element’s molar mass in grams is equal to its average atomic mass in amu.

An element’s molar mass can be used to convert from amount to mass, and vice versa.