The Periodic Table: Organizing the Elements

Dmitri Mendeleev ( ) constructed the first periodic table he listed the elements in columns in order of increasing atomic mass he arranged the elements according to similarities in their properties

Henry Moseley (1913) a British physicist who determined the atomic number of the atoms of the elements he arranged the elements in a table by order of atomic number instead of atomic mass

The Modern Periodic Table PERIODS - the horizontal rows of elements in the periodic table

Groups GROUP – the vertical column of elements in the periodic table ( 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A)

Group A Elements Group A elements are called REPRESENTATIVE ELEMENTS divided into 3 broad classes METALLOIDS NONMETALS METALS

Metals 1) METALS - have high electrical conductivity - high luster when clean - ductile ( can be drawn into wires) - malleable ( can be beaten into thin sheets)

Metals Group 1A – Alkali Metals (color them green) Group 2A- Alkaline Earth Metals (color them pink) Group B - Transition Metals & Inner Transition Metals ( Lathanide & Actinide Series) (color them orange)

Nonmetals 2) NONMETALS - occupy the upper-right corner of the periodic table - they are non-lustrous and poor conductors of electricity

Nonmetals Group 7A – Halogens (color them blue) Group 0 - Noble Gases (color them purple) (inert and undergo few chemical reactions)

Metalloids 3) METALLOIDS - elements that are intermediate between metals and non-metals (Ex. Silicon and Germanium)

Review- group names List an element that will have similar properties to Lithium.

Question Why do elements in a group have similar properties?

Elements in a group have similar electron configurations. Electron configuration- refers to how electrons are arranged around the nucleus.

Energy levels Energy Level- a layer or blanket of electrons Also referred to as an electron shell. Shells near the nucleus have less energy. Shells further away have more energy.

Question How are shells filled

Answer Shells with lower energy fill up first. Followed by outer shells.  1 st shell = space for two electrons  2 nd shell= space for 8 electrons  3 rd shell= space for 8 electrons

Valence shell- the outermost energy level of an atom. Contains the electrons that form chemical bonds Group number are the valence electron

Question How do I figure out the number of shells on an atom?

Answer Each period adds another energy level. Ex: Element in period (row) 3 have three layers of electrons.

How many energy levels does nitrogen have?

Answer Nitrogen is found in peroid 2 so it has 2 energy level

Question How do I figure out how many valance electrons an element has?

answer You look at the column number. 1A, 2A, 3A Count the boxes from left to right (skipping the transition metals)

Valence electron All elements in a column have the same number of valence electrons Thus they behave the same.

How many valance electrons do alkali metals have?

Answer Alkali metal are group one elements thus has one electron on the outer energy level One valance electron

Lewis Dot diagram Valence electrons are the most important in forming chemical bonds.

Lewis dot diagrams show only the valence electrons as dots surrounding the element symbol.

Example Chlorine is a group 7 element It has 7 valence electron Cl

Question How are the dots placed around the element

Answer Electron are place around the element from the top in a clockwise direction

Octet Rule The octet rule is a simple chemical rule of thumb that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells,chemicalrule of thumbatoms electronsvalence shells Giving them the same electronic configuration as a noble gas.electronic configurationnoble gas

Electron Dot Electron should be placed initially as lone pairs: one pair of dots for each pair of electrons available. Lone pairs should initially be placed on outer side of the element

Periodic Trends Atomic radii- the size of an atom From top to bottom atoms get bigger Why? More layers of electrons From left to right- Get smaller Why? More protons pull the electrons closer.

Atomic Radii

Electronegativity Electronegativity- ability to take electrons from another atom. From top to bottom- gets weaker From left to right gets stronger-

Electronegativity

Why do we care? Metals lose valance electrons Nonmetals take electrons Ionic bonds Covalent bonds Atoms near each other share electrons Non-metal with nonmetal