Patterns in the Periodic Table

Patterns in the Periodic Table: Periods and Groups We have seen the pattern of increasing atomic number and atomic weight as you go Also two other patterns: periods and groups Periods = horizontal rows Indicates number of electron shells the atoms of an element have All elements in a period have the same number of electrons shells Groups = vertical rows Indicates the number of valence electrons in the outer shell of the atoms of an element All elements in a group have the same number of valence electrons

Groups and Periods, Continued… On your Periodic Table, number the Periods and Groups

There are 3 Major Sections of Elements in the Periodic Table Most elements are metals. typically shiny good conductors of heat and electricity high density, and only melt at high temperatures ductile and malleable, so their shape can be easily changed into thin wires or sheets. Nonmetals, on the right side of the periodic table, are very different from metals. dull surface poor conductors of heat and electricity low density and will melt at low temperatures the shape of a nonmetal cannot be changed easily as they tend to be brittle and will break. Elements that have properties of both metals and nonmetals are called metalloids. shiny or dull shape is easily changed typically conduct heat and electricity better than nonmetals but not as well as metals.

Malleability and ductility State Appearance Conduc-tivity Malleability and ductility Metals Solid at room temp High density, only melt at high temps Exception: mercury (liquid) Shiny lustre Good conductors of heat and electricity Malleable and ductile, so shape can be easily changed into thin wires or sheets Non-Metals Some gases, some solids at room temp Low density, will melt at low temps Exception: bromine (liquid) Not very shiny Poor conductors of heat and electricity Brittle and not ductile, so shape cannot be easily changed Metalloids Solids at room temperature Can be shiny or dull May conduct electricity, but poor conductors of heat Brittle Not ductile

Metals, Metalloids and Non-Metals, Continued… Colour in each type of element. In black marker, indicate the “staircase” in the table that divides the metals from the nonmetals.

Chemical Reactivity and Ions Electrons in Motion Chemical Reactivity and Ions

Electrons move around the nucleus of an atom Electrons move around the nucleus of an atom. We depict them as being in orbits called shells that represent levels of energy. Ex. Be (Beryllium) Atomic # = 4 Electrons = 4 The first shell can only contain 2 electrons. The second shell contains 8 electrons. Subsequent shells contain sub-shells. The outermost shell is called the valence shell. The number of electrons here determines the element’s reactivity. So we know that… Periods indicate the total number of shells Groups (Families) indicate the number of valence electrons Reactivity indicates how easily the atoms will bond with others Be Period 2= 2 shells Group 2A = 2 valence electrons

Lewis Symbols Lewis symbols are also called “electron dot diagrams”. We use them to indicate the number of valence electrons the atoms of an element have. It’s a kind of a short-hand, instead of drawing all of the rings. It makes it easy to tell how reactive the element will be. Is palladium reactive?

Ex: sulfur (S) Atomic number = 16 Period 3 = 3 shells Group 16 (6A) = 6 valence electrons Lewis symbol

Ions Ions: atom or group of atoms that have an electric charge (+ or -) An ion is formed when an atom, or a group of atoms, lose or gain one or several electrons (e-) There are 2 types of ions: 1. cation: Positively charged ion, obtained when a neutral atom loses one or more electrons. 2. anion: Negatively charged ion, obtained when a neutral atom gains one or more electrons.

Sodium is an element whose atoms have only one valence electron Sodium is an element whose atoms have only one valence electron. The whole goal as an atom is to become a "Happy Atom“, which means having a full outer shell. A sodium ion (Na+) gives up its valence electron to have only ten electrons (but still 11 protons). That's the same number of electrons as neon (Ne). But it isn’t neon (Ne). Since it’s missing an electron it isn’t really a complete sodium (Na) atom either. It is something completely new. An ion. A cation more specifically. It has a positive charge because now there are more protons than electrons. The octet rule states that an atom wants 8 electrons in the valence shell to be complete. This makes it stable, and not reactive. Now that sodium has given up the electron, it is quite attractive... electrically, to other ions (negative or anions). Becoming an Ion…

Thinking About Patterns… Generally, Metals form positively charged ions (cations) Nonmetals form negatively charged ions (anions) Looking at the valence electrons, why does this pattern make sense?

Ex: N A nonmetal from group 15, it gains 3 electrons to form the anion N3- . N3- = N + 3 e- Ex: O A nonmetal from group 16, it gains 2 e- to become the anion O2- . O2- = O + 2 e- Ex: Na A metal from group 1, it loses 1 e- to become the cation Na+. Na+ = Na + 1 e-