Chapter 17: Properties of Atoms and the Periodic Table 17.1 – Structure of the Atom 17.2 – Masses of Atoms 17.3 – The Periodic Table

Symbols Chemical symbols have one capital letter, or one capital letter plus one or two small letters For some, the symbol is the first letter(s) of the elements name Some are named after scientists or for their properties Some come from Latin Ex. Argentum – Latin for “silver” (Ag on periodic table)

What are atoms? Atom: the smallest particle of an element that still retains the properties of the element (the element H only has H atoms) Atoms contain subatomic particles that affect its properties - nucleus – the center of the atom which contains protons, neutrons, and is surrounded by an electron cloud - protons – particles w/ a positive electrical charge (1+) - neutrons – particles that do not have an electrical charge - electrons – particles with a negative electrical charge (1-)

Atomic Model 400 B.C. – idea that atoms make up all substances Another Greek philosopher proposed that this was incorrect and matter was uniform throughout and not composed of smaller particles Finally in the 1800s, John Dalton proved that atoms exist Created the atomic model

Atoms Atoms are neutrally charged because the number of electrons is the same as the number of protons The atom of a given element may lose or gain electrons yet it still remains the same element The particles in the nucleus of an atom DO NOT change in a chemical reaction Chemical reactions occur in the electron cloud

Electron Cloud Model – the electron cloud is the area around the nucleus of an atom where its electrons are most likely found There is an attractive force between electrons and protons There is a repulsive forces between electrons and electrons/ protons and protons

How Much Do These Things Weigh? Most of the mass of an atom is contained within the nucleus of an atom Protons and neutrons each have a mass of 1.67 x 1024 grams Electrons have a mass about 2000 times smaller (1,836 exactly), therefore electrons are usually not considered when determining the mass of an atom ***You don’t have to know the exact mass of the particles

Quarks Scientists think electrons are not made of smaller particles – they themselves are one of the most basic types of particles Protons and neutrons are made up of quarks There are 6 different quarks 3 quarks held together – proton Another arrangement of 3 quarks – neutron Understanding the composition of protons and neutrons is an ongoing effort

Protons Identify the Element Protons identify the elements – If you are given the number of protons an element has in its nucleus, you can determine the name and symbol of the atom The number of protons in an atom is equal to the atomic number Example: an element with 7 protons will ALWAYS be Nitrogen (N) and an element with 79 protons will ALWAYS be Gold (Au) Please give the name and symbol for the following elements 14, 10, 1, 92

Further Identifying Atoms Mass Number = Number of Protons + Number of Neutrons (P+N) If you know the mass # and the atomic #, you can calculate the # of neutrons Isotopes – Atoms of the same element that have different numbers of neutrons (will always have the same number of protons) Ex. Carbon-12 and Carbon-14

Practice Complete the following table (MN = #P + #N) Element Symbol #P Atomic # #N Mass Number Silicon Si-29 14 15 29 Potassium K-40 Copper Cu-64 Krypton Kr-84 Remember the mass number is for a specific isotope and that the number of neutrons = mass number – number of protons

Average Atomic Mass The Atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes of an element. The atomic mass given on the periodic table is the average atomic mass. Why? Because there is usually more than one isotope of an given element.

Elements He-4 Symbol of the element Mass number

The Periodic Table Periodic – something that has a repeated pattern ex. Days of the week, 1st period followed by 2nd period… Dmitri Mendeleev – placed the known elements of his time in order of increasing atomic mass and found a pattern that repeated – followed predictable changes in physical & chemical properties Henry G.J. Mosely Improved the Periodic Table by placing elements according to atomic number, how it is today

Construction of the Periodic Table Groups – vertical columns on the periodic table (1-18) Elements in each group have similar properties Examples: Group #1 Hydrogen, Lithium, Sodium, etc. – highly reactive Group #11 (Copper, Silver, Gold) – shiny metal, good conductor of electricity and heat Group #18 “The Noble Gases” – non-reactive (except under certain conditions) non-metals

Electron Cloud Structure In a neutral atom, the number of electrons = the number of protons Electrons closer to the nucleus have lower amounts of energy, electrons further from the nucleus have more energy Elements in the same group have the same number of outer (valence electrons) which gives them similar properties (similar chemical reactivity)

Electron Cloud Structure There is a specific order in which the energy levels fill Energy Level 1 fills first with two electrons then it is full Energy Level 2 fills with eight electrons then it is full Energy Level 3 fills with eight electrons then it is full An atom is not stable unless it has a complete outer energy level (8 electrons)

Rows on the Periodic Table Periods on the periodic table of the elements run horizontally across the table Period numbers represent the number of energy levels an atom has

Regions (Families) on the Periodic Table of The Elements Alkali Metals (Group 1) Alkaline Earth Metals (Group 2) Transition Metals (Groups 3-12) Metalloids (Stair step Line) Non-Metals (To the Right of the stairs) Noble gases (Group 18) Lanthanide Series (Elements 58-71) Actinide Series (Elements 90-104 + Radioactive)

Valence Electrons The number of electrons in the outer-most energy level are called valence electrons Group Name # valence electrons 1 Alkali Metals 2 Alkaline Earth Metals 13 3 14 4 15 5 16 Oxygen Group 6 17 Halogens 7 18 Noble Gases 8 (except He)

Trend in The Periodic Table Trends in the number of valence electrons From L to R From Top to Bottom Trends in the number of energy levels From left to right across any period From top to bottom within any group

Atoms Stable atoms contain 8 valence electrons – If an atom does not have 8, it tends to gain, lose, or share valence electrons to become stable Group 1 & 2 : lose 1 and 2 electrons, respectively Group 18 : stable, do not readily gain/lose Group 16 & 17 : gain 2 and 1 electrons, respectively Group 13-15: less likely to gain/lose Most transition elements (Groups 3-12) : tend to lose electrons