Chapter Fifteen: Elements and

the Periodic Table15.1 The Periodic Table of the Elements

15.2 Properties of the Elements

15.1 Physical properties

Characteristics that you can see through direct observation are called physical properties.

Physical properties include color, texture, density, brittleness, and state (solid, liquid, or gas).

Melting point, boiling point, and specific heat are also physical properties.

15.1 Physical properties

A physical change does not result in a new substance being formed.

15.1 Chemical propertiesProperties that can only be observed

when one substance changes into a different substance are called chemical properties.

Any change that transforms one substance into a different substance is called a chemical change.

15.1 The Periodic Table

The periodic table organizes the elements according to how they combine with other elements (chemical properties).

The periodic table is organized in order of increasing atomic number.

15.1 The Periodic TableThe periodic table

is further divided into periods and groups.

Each horizontal row is called a period.

Each vertical column is called a group.

15.1 The Periodic TableAll the elements in

Group 1 of the periodic table form similar compounds.

The metals lithium, sodium, and potassium all form compounds with a ratio of 2 atoms of the metal to 1 atom of oxygen.

15.1 Atomic MassThe mass of individual atoms is so small that the numbers are difficult to work with.

To make calculations easier, scientists use the atomic mass unit (amu).

The atomic mass of any element is the average mass (in amu) of an atom of each element.

15.1 Atomic MassAtomic masses differ from mass numbers because most elements in nature contain more than one isotope.

15.1 Atomic Number Remember, the atomic number is the

number of protons all atoms of that element have in their nuclei.

If the atom is neutral, it will have the same number of electrons as protons.

15.1 Groups of the periodic tableThe first group is known as the

alkali metals. The alkali metals are soft and silvery in their pure form and are highly reactive.

This group includes the elements lithium (Li), sodium (Na), and potassium (K).

15.1 Groups of the periodic tableThe group two metals include

beryllium (Be), magnesium (Mg), and calcium (Ca).

They also bond easily with oxygen.

15.1 HalogensThe halogens tend to be toxic gases or liquids in their pure form.

Fluorine (F), chlorine (Cl), and bromine (Br) form salts when the bond with alkali metals.

15.1 Noble GasesThe noble gases, including the elements helium (He), neon (Ne), and argon (Ar).

These elements do not naturally form chemical bonds with other atoms and are almost always found in their pure state.

15.2 Properties of the elementsMost of the pure elements are

solid at room temperature.

Only 11 naturally occurring elements are a gas.

Only 2 elements (Br and Hg) are liquid at room temperature.

15.2 Periodic properties of elements

Periodicity means properties repeat each period (row) of the periodic table.

15.2 Thermal and electrical conductivity

Electricity is the movement of electric charge, usually electrons.

Some materials allow electrons to flow easily through them.

We call these materials electrical conductors.

15.2 Thermal and electrical conductivity

Like copper, most metals are good thermal conductors.

That is one reason pots and pans are made of metal.

15.2 Thermal and electrical conductivity

Elements on the far right of the table are called non-metals.

Nonmetals make good insulators.

An insulator is a material which slows down or stops the flow of either heat or electricity.

15.2 Metals and metal alloys

An alloy is a solid mixture of one or more elements.

Most metals are used as alloys and not in their pure elemental form.

Yellow brass is an alloy of 72% copper, 24% zinc, 3% lead, and 1% tin.

15.2 Metals and metal alloysTitanium combines the

strength and hardness of steel with the light weight of aluminum.

Titanium, a rare and expensive alloy, is used for military aircraft and racing bicycles.

15.2 Carbon and carbon-like elements

Almost all the molecules that make up plants and animals are constructed around carbon.

The chemistry of carbon is so important it has its own name, organic chemistry.

15.2 Carbon and carbon-like elements

Pure carbon is found in nature as either graphite or diamond.

Silicon is the second most abundant element in the Earth’s crust, second only to oxygen.

Why are carbon and silicon important?

15.2 Nitrogen, oxygen and phosphorus

Oxygen and nitrogen are crucial to living animals and plants.

For example, proteins and DNA both contain nitrogen.

Phosphorus is a key ingredient of DNA, the molecule responsible for carrying the genetic code in all living creatures.

15.2 Nitrogen, oxygen and phosphorus

Proteins and DNA both contain oxygen and nitrogen, making these elements crucial to life.

46% of the mass of Earth’s crust is also oxygen bound up in rocks and minerals.

15.2 Nitrogen, oxygen and phosphorus

Phosphorus is a key ingredient of DNA, the molecule responsible for carrying the genetic code in all living creatures.

When phosphorus atoms absorb light, they store energy, then release it in a greenish glow.