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 1 st energy level – 2 electrons 2 nd energy level – 8 electrons 3 rd 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. (Mass 1 x % Isotope 1 ) + (Mass 2 x % Isotope 2 ) + (etc.)

Average Atomic Mass 43.00% of 74.2 amu; 57.00% of 77.1 amu (Mass 1 x % Isotope 1 ) + (Mass 2 x % Isotope 2 ) + (etc.) (74.2 amu x 43.00) + (77.1 amu x 57.00) ( amu) + ( amu) amu amu 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