Chapter 3 Elements and the Periodic Table

Structure of an Atom Protons and neutrons have about equal mass Nucleus: small center core of an atom. Protons: positively charged atom Neutrons: particles with no charge + + e - + Protons and neutrons have about equal mass Together the protons and neutrons make up most of the atoms mass. Nucleus

Electrons: negatively charged particles that move rapidly around the nucleus Electron cloud: the space around the nucleus where the electrons are located. Accounts for most of the atoms volume. Electrons have the smallest mass They have distinct amounts of energy …. higher energy electrons are farther away from the nucleus Lower energy electrons are closer to the nucleus.

In an atom: the number of protons = the number of electrons. The number of neutrons can be different.

Elements can be identified by the number of protons in the nucleus of its atom. Atomic Number: the number of protons in its nucleus. The number of protons identifies the atom. Example: Oxygen has an atomic number of 8 Mass Number: the sum of the protons and neutrons in the nucleus of an atom. 8 O Oxygen 15.999

To determine the number of neutrons in an atom: Mass Number – Atomic Number = # of Neutrons. 3 Li Lithium 6.941 Example: Lithium has an atomic number of 3 and a mass number of 6.941 which we round to 7. Mass Number – Atomic Number = # of Neutrons 7 - 3 = 4 Neutrons Therefore…. Lithium has: 3 protons and 4 neutrons What about electrons?????? Remember: neutral atoms (atoms with no charge) have an equal number of protons and electrons…… Therefore..... Lithium has: 3 electrons.

Element Symbol Atomic # Atomic Mass Protons Neutrons Electrons Lithium Li 3 7 4 Phosphorous P 15 31 16 Chlorine Cl 17 35 18 Potassium K 19 39 20 Silver Ag 47 108 61 Silicon Si 14 28 Hydrogen H 1

Isotopes: Atoms that have the same number of protons but different numbers of neutrons. Example: Carbon always has 6 protons, but may have 6, 7, or 8 neutrons. Common notations for isotopes of Carbon with 8 neutrons are C-14, Carbon- 14 or 14C

Bohr Model A model used to show energy levels and where electrons may be located around the nucleus. The energy level closest to the nucleus holds 2 electrons The next energy level holds 8 electrons. The third energy level can hold up to 18 electrons. The last energy level holds electrons called valence electrons

To Draw a Bohr Diagram: Find your element on the periodic table. Inside the nucleus write the number of protons and number of neutrons (determine by subtracting atomic number and atomic mass.) Determine the number of electrons – it is the same as the atomic number. This is how many electrons you will draw.

Carbon has an atomic number of 6 You will draw 6 electrons. Remember your rules, the first shell can only have 2 electrons. The remaining 4 electrons will go into the next energy level. 6 P 6 N

Valence electrons the outermost electrons from the nucleus. The number of valence electrons give the element its chemical properties. The greatest number of valence electrons for any atom is 8. These electrons play a role in chemical bonding between atoms to form molecules.

Organizing Elements

Dmitri Mendeleev a Russian scientist who discovered a set of patterns that applied to all the elements. He noticed a pattern or properties appeared when he arranged the elements in order of increasing atomic mass.

The Modern Periodic Table New elements have been added since Medeleev’s table. Elements are arranged in order of increasing atomic number Contains one square for each element

26 Fe Iron 55.847 Atomic Number Symbol Element Atomic Mass Number

The Properties of an element can be predicted from its location in the periodic table. Periods: the horizontal rows (colored pink) Numbered 1-7 The elements have the same # of valence shells.

Across the Periodic Table Periods: Are arranged horizontally across the periodic table (rows 1-7) These elements have the same number of valence shells. 2nd Period 6th Period

Groups: the vertical columns (colored blue) Also called families Elements have similar characteristics Numbered 1-18 The number of valence electrons is the same for all elements in a group

Down the Periodic Table Family: Are arranged vertically down the periodic table (columns or group, 1- 18 or 1-8 A,B) These elements have the same number electrons in the outer most shells, the valence shell. Alkali Family: 1 e- in the valence shell Halogen Family: 7 e- in the valence shell

Lewis Structures Find your element on the periodic table. Determine the number of valence electrons. This is how many electrons you will draw.

Lewis Structures Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons. www.chem4kids.com

Groups Group 13 = 3 ve Group 14 = 4 ve Group 15 = 5 ve (except He) Group 1 = 1 electron Group 2 = 2 electrons www.chem4kids.com

C Lewis Structures Write the element symbol. Carbon is in the 14th group, so it has 4 valence electrons. Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol. C

C Lewis Structures Check your work. Using your periodic table, check that Carbon is in the 14th group. You should have 4 total electrons, or dots, drawn in for Carbon. C

Li Ne Mg Cl

Periodic Table: Metallic arrangement Layout of the Periodic Table: Metals vs. nonmetals Nonmetals Metals

Infamous Families of the Periodic Table Notable families of the Periodic Table and some important members: Alkali Alkaline (earth) Transition Metals Noble Gas Halogen Chalcogens

Properties of Metals Shiny Malleable : can be hammered or rolled into flat sheets and other shapes Ductile: can be pulled out or drawn into a long wire. Conductive: the ability of an object to transfer heat or electricity to another object. Reactive: they combine or react with other elements easily. A chemical property of metal is its reaction with water which results in corrosion.

Alkali metals: metals in Group 1 Hydrogen is NOT a member (it is not a metal) React with other elements by losing one electron. So reactive that they are never found uncombined in nature. They are only found in compounds. Very reactive with water. Shiny and soft so that you can cut with a knife. Examples: sodium (Na), Lithium (Li), Potassium (K)

Alkaline Earth Metals: metals in Group 2 Fairly hard, gray-white metals Good conductors of electricity React by losing 2 electrons Not as reactive as Group 1 elements Never found uncombined in nature. Examples: beryllium, magnesium, calcium, barium

Transition metals Groups 3 – 12 Most are hard and shiny Good conductors of electricity Less reactive then group 1 and 2 Examples: Iron, copper, nickel, gold, silver

Metals in Groups 13-15 Not as reactive as metals on the right side of the periodic table. Aluminum, tin, lead

Lanthanides Top row on bottom of periodic table Soft, malleable, shiny, high conductivity Usually mixed with other elements to form alloys: a mixture of metal with at least one other element. Actinides: Bottom row of bottom of periodic table Some are created in a lab. Some exist in nature

Nonmetals: element that lacks most of the properties of a metal Physical Properties Poor conductors of electricity and heat Reactive with other elements Solid nonmetals are dull and brittle, not malleable and ductile Have lower densities than metals 10 of the 16 are gases at room temperature   Chemical Properties Reactive and gain or share electrons when they react with other atoms.

Metalloids: elements that have characteristics of both metals and nonmetals Properties (physical and chemical) All are solid at room temperature Brittle, hard and somewhat reactive Most useful property is their varying ability to conduct electricity. Used to make semiconductors: substances that can conduct electricity under some conditions but not under other conditions. Used to make computer chips, lasers and transistors

BORON FAMILY Group 13 3 valence electrons in the outer shell Most are metals: Aluminum, Gallium, Indium Thallium Metalloid: Boron

CARBON FAMILY Group 14 4 valence electrons Atoms can gain, lose or share 4 electrons Non-metal: Carbon (C) Metalloids: silicon, germanium Metals: Tin and lead

NITROGEN FAMILY Group 15 5 valence electrons in the outer shell Can gain or share 3 electrons to form compounds Non-metals: Nitrogen, phosphorous, Metalloids: arsenic, antimony Metals: bismuth

OXYGEN FAMILY Group 16 6 valence electrons in the outer shell Can gain or share 2 electrons Reactive Nonmetals: Oxygen, sulfur, selenium Metalloids: Tellurium Polonium Metals: none

Halogens (salt forming) Group 17 7 valence electrons in the outer shell Can gain or share 1 electron Very reactive are often bonded with elements from Group 1 Nonmetals: Flourine, chlorine, bromine, iodine Metalloids: Astatine Metals: none

Noble Gases Group 18 Exist as gases 8 valence electrons in the outer shell = Full Helium (He) has only 2 electrons in the outer shell = Full Not reactive with other elements Non-metals: Helium, neon, argon, krypton, xenon, radon No metalloids or metals