Chapter 5Chapter 5Chapter 5Chapter 5

The Periodic TableThe Periodic Table

5-1 Organizing the Elements

• What does the word “periodic” mean?

• Periodic: recurring at regular intervals

• Periodic table – is an arrangement of elements in columns based on a set of properties that repeat from row to row

Mendeleev 1869• See Figure 3 on page 127• Arranged elements according to

increasing atomic mass in rows• Put elements of similar properties in the

same column• Left blank spots in table which predicted

properties of elements not yet discovered

Evidence Supporting Mendeleev’s Table

• Named eka-aluminum to the element that belonged one space below aluminum on the table

• 1875- French chemist discovered a new element and named it gallium (Ga)

• Gallium is a soft metal used in traffic signals

Similarity of the two• Eka-aluminum and Gallium were

similar in properties, so they were determined to be the same

• The close match between Mendeleev’s prediction and the actual properties of new elements showed how useful his periodic table could be

Questions1. Which of the following is a

symbol for an element?a. Aluminumb. Alc. ald. AL

Questions3. What happens to the composition

of matter during a physical change? Does it change or remain the same?

Questions2. Is flammability a physical

property or a chemical property?

Questions4. What does the atomic number of

an element represent?

Question5. Isotopes of element have

different numbers ofa. Neutronsb. Electronsc. Protonsd. nuclei

Question6. True or False : Electrons in atoms

occupy orbitals in energy levels

5-2 The Modern Periodic Table

• Mendeleev developed the periodic table before the discovery of protons.

• In the modern periodic table, elements are arranged by increasing atomic number

Periods • Each row in the table of elements is called a

period• Period 1 has two elements • Periods 2 and 3 have 8 elements• Periods 4 and 5 have 18 elements• Period 6 has 32 elements• There are 7 periods total on the periodic table• The number of electrons per period varies

because of the number of available orbitals increases from energy level to energy level

Groups• Each column on the periodic table is called a

group• The elements within a group have similar

properties• Properties of elements repeat in a predicable

way when atomic number are used to arrange elements into groups

• The pattern of repeating properties is the periodic law

• There are 18 groups on the periodic table

Atomic Mass• Atomic mass is a value that

depends on the distribution of an element’s isotopes in nature and the masses of those isotopes

• An atomic mass unit (amu) is defined as one twelfth the mass of carbon-12 atom

Average Atomic Mass

•Weighted average of the atomic masses of the naturally occurring isotopes of an element

What is the aver. atomic mass of the

chlorine?

Isotope Isotope Mass (amu)

% Abundance

Chlorine-35

34.96885 75.771

Chlorine-37

36.96590 24.229

Weighted Averages• Average Atomic Mass = • (isotope mass)(relative abundance[dec]) + (isotope mass)(relative abundance[dec])

• (0.75771)(34.96885amu) + (0.24229)(36.96590amu)

• = 35.453 amu

ISOTOPES • Atoms of the same element that

differ in mass• Have the same # protons but

different # neutrons

Classes of Elements• Elements are classified as metals, nonmetals, and metalloids

• Metal:– Good conductor of heat & electricity– Ductile –able to be drawn into a fine wire– Malleability – can be hammered or rolled into thin sheets

• Nonmetal– Poor conductor of heat & electricity– Brittle

• Metalloids– Some characteristics of metals & nonmetals

Beaker Breaker1. Isotopes have the same # of _______

but different #of __________

2. What is the name of group 1 on the periodic table?

3. How many periods are there on the periodic table?

Transition Metals• Transition metals are elements

that form a bridge between the elements on the left and right sides of the table

The Lanthanides• The 14 elements with atomic

numbers from 58(cerium, Ce) to 71(lutetium, Lr)

• Similar in chemical and physical properties

The Actinides• The 14 elements with atomic

number from 90(thorium, Th) to 103(lawrencium, Lr)

Variation across a period

• Across a period from left to right, the elements become less metallic and more nonmetallic in their properties

• Most reactive metals are on the left side of the table

• Most reactive nonmetals are on the right in Group 17

5-3 Representative Groups

• Valence electron – is an electron that is in the highest occupied energy level of an atom

• Elements in a group have similar properties because they have the same number of valence electrons

• Valence electrons explain the location of hydrogen, hydrogen has a single electron

Alkali Metals• Elements in Group 1A are called

alkali metals.• Single valence electron and are

extremely reactive• The reactivity of alkali metals

increases from the top of Group 1A to the bottom

The Alkaline Earth Metals

• The elements in Group 2A are called alkaline earth metals

• All alkaline earth metals have two valence electrons

• They are harder than group 1A

• Differences in reactivity among the alkaline earth metals are shown by the ways they react with water

• Calcium, strontium and barium react easily with cold water

• Magnesium will react with hot water. No change appears to occur when beryllium is added to water

The Boron Family• Group 3A contains the metalloid

boron.• Aluminum is the most abundant

metal in the Earth’s crust• Glass that contains boron is used

to make laboratory glassware such as flasks

The Carbon Family• Group 4A contains nonmetal carbon• Two metalloids – silicon and germanium• Two metals – lead and tin• Except for water, most of the

compounds in your body contains carbon• Silicon is the second most abundant

element in the Earth’s crust

The Nitrogen Family• Group 5A contains two nonmetals

– nitrogen and phosphorus• Two metalloids – arsenic and

antimony• One metal –bismuth• Besides nitrogen, fertilizers often

contain phosphorus

The Oxygen Family• Group 6A has three nonmetals –

oxygen, sulfur, and selenium• Two metalloids – tellurium and

polonium• All have 6 valence electrons• Oxygen is the most abundant

element in the Earth’s crust

The Halogens• The elements in Group 7A are called

halogens• They have seven valence electrons• Despite their physical differences, the

halogens have similar chemical properties

• They are highly reactive nonmetals• Fluorine is the most reactive

The Noble Gases• The elements in Group 8A are called

the noble gases• Helium has 2 valence electrons• All other noble gases have 8 valence

electrons• The noble gases are colorless and

odorless and extremely unreactive• All the noble gases except radon are

used in “neon” lights