Chapter 17Properties of Atoms & the Periodic Table

Symbols of Elements

• Symbols are used to represent 1 atom of an element

• Each element has its own symbol

• The symbol is 1 to 3 characters

• The first letter is always capitalized, the second and third letters are always lower case

• Three-letter symbols are to represent represent man-made elements that have not officially been named yet (Example: Uup for ununpentium, 115)

Symbols of Elements (Cont.)• Many of the symbols are the first letter of the name

(Examples: H for hydrogen, O for oxygen).

• The second letter (if there is one) is one that you hear (Example: Ca for calcium, Cl for chlorine).

• Some symbols are derived from their Latin name (Example: Fe [ferrum] for iron, Na [natrium] for sodium Ag [argentum] for silver).

Symbols of Elements (Cont.)• This is a world-wide system, so scientists across the

world use this (even people who don’t use English letters in their language).

• H stands for 1 atom of hydrogen, 2H represents 2 atoms of hydrogen, H2 represents two atoms of hydrogen bonded together.

Atomic Components

• An element is matter that is made of one type of atom (hydrogen is made of hydrogen atoms).

• Atoms have three major subatomic particles.

• Protons - positive particles (+1) that are in the center of the atom (nucleus) and have a mass of 1 atomic mass unit (1 amu)

Atomic Components (cont.)• 3 Major Subatomic Particles (continued)

• Neutrons - neutral particles that are in the nucleus and have a mass of 1 amu

• Electrons - negative particles (-1) that orbit the nucleus, have a mass of 1/2000 amu (basically 0 amu)

Electron Cloud Model• An electron cloud is the area

around the nucleus of an atom where its electrons are most likely found.!

• The electron cloud is 100,000 times larger than the nucleus. !

• The electrons are moving at high speeds around the nucleus.

Atomic Number

• The number of protons identify the element. If an atom has one proton it is hydrogen, if it has two protons it is helium, if it has three protons it is lithium, and so on.

• The number of protons is called the atomic number, so the atomic number of hydrogen is one, the atomic number of helium is two, and the atomic number of lithium is three.

Mass Number

• The mass number is defined as the number of protons plus the number of neutrons in the nucleus.

• mass number = # protons + # neutrons

• If an atom of lithium has 3 protons and 4 neutrons, then -

• Mass number of lithium = 3 + 4 = 7

Isotopes• Isotopes are

• atoms with the same number of protons, but with different number of neutrons, or

• atoms with the same atomic number but different mass number.

Calculating Numbers of Subatomic Particles

ISOTOPE ATOMIC NUMBER

MASS NUMBER

# PROTONS

# NEUTRONS

# ELECTRONS

BORON-10 5 10 5 5 5

BORON-11 5 11 5 6 5

CARBON-12 6 12 6 6 6

CARBON-14 6 14 6 8 6

The Atom & The Periodic Table

• The periodic table groups elements by the location of their electrons and their properties.

• Columns (vertical) in the periodic table are called GROUPS or FAMILIES. They have the same number of electrons in their outer energy levels, and they have similar chemical properties.

• For example, column 1 is called the sodium family or alkali metals. They are all very reactive, and except for hydrogen, they are all soft metals that react vigorously with water. They all have 1 electron in their outer energy level.

The Atom & The Periodic Table (Cont.)

• Rows (horizontal) in the periodic table are called PERIODS, and the number to the left shows which energy level electrons are being added to.

• For example, hydrogen and helium are in row 1, and their electrons are in the 1st energy level.

• Lithium through neon are in row 2, and their outer electrons are in the 2nd energy level.

Energy Levels• An ENERGY LEVEL is a region in the electron cloud

where electrons with similar energies orbit.

• The elections in the 1st energy level have the least amount of energy, 2nd energy level has more energy, and the 3rd has even more. This is similar to a set of steps, where it takes more energy to move up a step.

Energy Levels (Cont.)• Electrons occupy the lowest energy level possible, but

only so many electrons can fit into an energy level. The graphic below shows those electrons.

• The next slide shows the maximum number of electrons possible for the first four energy levels.

Energy LevelsENERGY LEVEL NUMBER OF ELECTRONS

POSSIBLE

1 2

2 8

3 18

4 32

Electrons & Energy Levels• Using the chart below, ask yourself how electrons an

atom of boron has, and where they are located.

• Answer: Boron has 5 elections - there are two in the 1st energy level, and 3 in the 2nd energy level.

Electrons & Energy Levels (Continued)

• Using the chart below, ask yourself how electrons and atom of fluorine has, and where they are located.

• Answer: Fluorine has 9 elections - there are two in the 1st energy level, and 7 in the 2nd energy level.

Electrons & Energy Levels (Continued)

• Using the chart below, ask yourself how electrons and atom of sulfur has, and where they are located.

• Answer: Sulfur has 16 elections - there are two in the 1st energy level, 8 in the 2nd energy level, and 6 in the third energy level.