Chapter 19 – Properties of Atoms & Chapter 19 – Properties of Atoms & the Periodic Tablethe Periodic Table

Chapter previewChapter previewsectionssections

1 Structure of the Atom

2 Masses of Atoms

3 The Periodic Table

Atoms Compose All Things, Great and SmallEverything in the universe is composed of tiny

particles called atoms. You will learn about atoms and their components:

protons, neutrons, electrons, and quarks.

Properties of Atoms and the Properties of Atoms and the Periodic TablePeriodic Table

Section 1—Structure of the Atom

Original Author: Donna Myers

Scientific Shorthand

Elements are abbreviated in scientific shorthand.

Consist of one capital letter or a capital letter plus one or two small letters.

Some symbols are derived from Latin.• Argentum is Latin for “silver”

Learn Table 1 on page 578

Symbols of Some ElementsElement Symbol Element Symbol Element Symbol

Aluminum Al Gold Au Mercury Hg

Calcium Ca Helium He Nitrogen N

Carbon C Hydrogen H Oxygen O

Chlorine Cl Iodine I Potassium K

Copper Cu Iron Fe Silver Ag

Fluorine F Magnesium Mg Sodium Na

Atom

An element is matter that is composed of one type of atom.

Atom is the smallest piece of matter that still has the properties of the element.

A chemical symbol represents the name of an element.

Atomic Components

Protons—particles with electrical charge of 1+

Neutrons—neutral particles with no electrical charge.

Electrons—particles with electrical charge of 1–

Nucleus—positively charged central core of the atom

Atomic components

• Protons and neutrons are in center of nucleus.

• The region around the nucleus occupied by electrons is called the electron cloud.

Quarks The nucleus of the atom

contains protons and neutrons that are composed of particles of matter called quarks.

Six quarks are known to exist.

Quarks are studied by colliding accelerated charged particles with protons, which leave tracks in a bubble chamber.

Bubble chamber image Bubble chamber

Tevatron

A tevatron is used to accelerate protons in the study of subatomic particles.

Models

Scientists use scale-up models to represent atoms.

John Dalton’s atomic model was a simple sphere.

NATIONAL

GEOGRAPHIC The ancient Greek philosopher Democritis

proposed that elements consist of tiny, solid particles that cannot be subdivided.

Democritis’s Uncuttable Atom

Thompson Model, 1904

Rutherford Model, 1911

Bohr Model, 1913

Visualizing theAtomic Model

See Figure 5, page 582

The Electron Cloud Model (Current)

In 1926, scientists developed the electron cloud model of the atom that is used today.

This model shows electrons traveling in specific energy levels around a nucleus of protons and neutrons.

According to present atomic theory, the location of an electron in an atom cannot be pinpointed exactly.

Masses of AtomsMasses of Atoms

Section 2

Atomic Mass

Composed mostly of protons and neutrons.

Majority of the mass of an atom is located in the nucleus.

Atomic Mass Units

Unit of measurement for atomic particles is atomic mass unit (amu) which is one-twelfth the mass of a carbon atom containing six protons and six neutrons.

1 amu = mass of 1 proton or 1 neutron

Comparison of Particles in an Atom

Protons and neutrons are about the same size and mass.

Electrons are about 1,836 times smaller than protons and neutrons.

Atomic Number

Protons identify the element.

Mass Number

The sum of the number of protons and neutrons in an atom• Protons + neutrons = mass number

• A certain atom has 26 protons, 26 electrons, and 30 neutrons. What is its mass number?

Mass Numbers of Some Atoms (page 585)

Element Symbol Atomic Number

Protons Neutrons Mass Number

Average Atomic Mass

Boron B 5 5 6 11 10.81

Carbon C 6 6 6 12 12.01

Oxygen O 8 8 8 16 16.00

Sodium Na 11 11 12 23 22.99

Copper Cu 29 29 34 63 63.55

Isotopes

Atoms of the same element with different numbers of neutrons.

Different isotopes have different properties. Name of element followed by mass number

identifies the isotope.• Carbon-12

• Carbon-14

• Lead-206

Isotopes

To find number of neutrons:• mass number – atomic number =

number of neutrons

Atoms of boron have mass numbers of 10 or 11. How many neutrons are in a boron atom?• Boron-10 10 – 5 = 5 neutrons

• Boron-11 11 – 5 = 6 neutrons

Average Atomic Mass

The average atomic mass is the weighted-average mass of the mixture of its isotopes.

Average atomic mass is closest to its most abundant isotope.

Four out of five atoms of boron are boron-11 and one out of five is boron-10

Average atomic mass of boron is close to mass of most abundant isotope, boron-11.

Isotopes

The average mass is closest to its most abundant isotope• Chlorine’s atomic mass is 35.453. List two

possible isotopes of chlorine.• Cl-35 and Cl-36

Work Section 2 Assessment, page 587

1) Use paper and pencil (colored if you have them) to draw the electron cloud model for lithium. Include the correct number of protons and electrons. Include four neutrons in the drawing.

2) Calculate the weighted average of the following quiz scores: 5 students scored 80%; 19 students scored 90%.

The Periodic TableThe Periodic TableSection 3Section 3

Periodic Table

The modern day periodic table is a chart showing the classifications of elements according to their properties and increasing atomic numbers.

The p. t. is useful because it shows the relationship among the elements and it can be used to predict similarities and differences among the elements.

Dmitri Mendeleev

Developed the first periodic table He arranged the elements by increasing

atomic mass and aligned them in columns based on chemical and physical properties.

Groups On The Periodic Table

Elements arranged in Elements arranged in verticalvertical columns in columns in the periodic tablethe periodic table

Elements in a group have Elements in a group have similar similar propertiesproperties

Elements in a group have the same Elements in a group have the same number of electronsnumber of electrons in their outer energy in their outer energy level.level.

There are 18 groupsThere are 18 groups

Energy Levels

There are 7 energy levels Energy level one contains a maximum of

2 electrons Maximum number of electrons in

second energy level is 8. Each row in the periodic table ends when

an outer energy level is filled.

Major energy level K L M N O P Q

Maximum number of electrons

2 8 18 32 32 18 2

Noble Gases

Group 8A on periodic table A complete and very stable electron

arrangement in the outer energy level will contain 8 electrons—this very stable arrangement is characteristic of noble gases.

Electron Dot Diagrams

Are used to show how electrons in the outer energy level are bonded when elements combine to form compounds.

Periods

Horizontal rows of elements that contain increasing numbers of protons and electrons.

One proton and one electron are added to each element as you go across the periodic table from left to right.

Classification of Elements All elements in yellow squares are metals. All elements in green squares are nonmetals All elements in purple squares are metalloids or

semimetal.

Properties of Metals

Most metals exist as solids at room temperature

They are shiny, can be drawn into wires, pounded into sheets, and are good conductors of electricity.

Moving from left to right in a row of the periodic table, metallic properties of atoms decrease.

Properties of Nonmetals and Metalloids

Nonmetals—• Most are gases

• Brittle

• Poor conductors of heat and electricity

Metalloids• Have some properties

of both metals and nonmetals

Chlorine gas

Boron and silicon

Elements in the Universe All elements

throughout the universe are the same.

Hydrogen and helium are the building blocks of other naturally occurring elements.

Scientist believe that naturally occurring elements are manufactured within stars.