Properties of Atoms and the Periodic Table

Chapter 18

18-1: Structure of the Atom

Atoms

Atom – the smallest unit of matter that can’t be broken down by chemical means

Atoms are made up of three types of particles: Proton: (+) charged Neutron: no charge Electron: (-) charged

Nucleus – consists of protons and neutrons

Atoms

A proton is about 1000 times larger than an electron

Electron cloud – the region where electrons orbit the nucleus

18-2: Masses of Atoms

Atomic Mass

Atomic mass = protons + neutrons

Atomic number - The number of protons in the nucleus of an atom, which determines its place in the periodic table

Atomic Mass

Atomic Facts Atomic number = protons = electrons

Atomic mass

- Atomic number # of neutrons

Maximum number of electrons 1st energy level – 2 electrons 2nd energy level – 8 electrons 3rd energy level – 18 electrons

Atomic Mass

Element – A substance made up a group of similar atoms that have the same number of protons

Atomic Mass

Isotopes – Atoms of an element that have different numbers of neutrons

Chemical Bonds

Valence electron – An electron that is found in the outermost shell of an atom Lewis dot diagrams can be used to show the

transfer of valence electrons

Chemical Bonds

Chemical bonds form between groups of atoms because most atoms become stable when they have eight electrons in the valence shell (Octet rule)

Chemical Bonds

Compound – A substance made of the bonded atoms of two or more different elements

Chemical Bonds

Ion – an atom or group of atoms that has an electric charge because it has gained or lost electrons Ionic bond – the attractive force between

oppositely charged ions

Chemical Bonds

Covalent bond – chemical bond that shares electrons

Molecule – A group of atoms held together by covalent bonds

Chemical Bonds

Hydrogen bond - A chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom

Chemical Bonds

Polarity

Polar – molecules with partial charges on opposite ends

Water is the most abundant compound in organisms

Average Atomic Mass

Average atomic mass is not a straight average but a weighted average based upon the percent isotopic ratio of the element.

(Mass1 x % Isotope1) + (Mass2 x % Isotope2) + (etc.)

100 100

Average Atomic Mass

43.00% of 74.2 amu; 57.00% of 77.1 amu (Mass1 x % Isotope1) + (Mass2 x % Isotope2) + (etc.)

100 100 (74.2 amu x 43.00) + (77.1 amu x 57.00)

100 100 (3190.6 amu) + (4394.7 amu)

100 100 31.906 amu + 43.947 amu 75.853 amu

18-3: The Periodic Table

The Periodic Law

The modern periodic table is based on atomic number, or number of protons.

The Periodic Law

Period – Each row in the table of elements Hydrogen, the first element in Period 1, has one

electron in its first energy level. Lithium, the first element in Period 2, has one

electron in its second energy level.

The Periodic Law

Group – Each column in the periodic table The elements in a group have similar electron

configurations

The Periodic Law

Classes of Elements

Metals – elements that are good conductors of electric current and heat Except for mercury, metals are solids at room

temperature

Classes of Elements

Metals (cont.) Malleable – able to be hammered or pressed

permanently out of shape without breaking or cracking

Ductile – can be drawn into thin wires

Classes of Elements

Transition metals – elements that form a bridge between the elements on the left and right sides of the table Many of their compounds are colored

Classes of Elements

Nonmetals – elements that are poor conductors of heat and electric current Many nonmetals are gases at room temperature Nonmetals that are solids at room temperature

tend to be brittle Brittle – hard but liable to break or shatter easily

Classes of Elements

Metalloids – elements with properties that fall between those of metals and nonmetals

18-3: Representative Groups

Representative Groups

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

Representative Groups

Alkali metals – (Group 1A) These metals have a single valence electron and are extremely reactive

Representative Groups

Alkaline earth metals (Group 2A) – have two valence electrons

Representative Groups

Boron family (Group 3A) – have three valence electrons

Representative Groups

Carbon family (Group 4A) – have four valence electrons Clay used to

produce this

pottery contains

silicon

Representative Groups

Nitrogen family (Group 5A) – have five valence electrons

The numbers on the bags of fertilizer are, from left to right, the relative amounts of nitrogen, phosphorus, and potassium.

Representative Groups

Oxygen family

(Chalcogen) –

(Group 6A) have six

valence electrons

Representative Groups

Halogens (Group 7A) – have seven valence electrons

Representative Groups

Noble gases (Group 8A) – Helium has two valence electrons. Each of the other noble gases has eight valence electrons.

Noble gases are extremely

unreactive