Introductory Chemistry, 3rd Edition Nivaldo Tro Intro to the Periodic Table And Atoms Vs. Ions Isotopes

The Modern Atom Atoms are composed of three particles - protons, neutrons and electrons The nucleus contains protons and neutrons The electrons move outside the nucleus Neutral atom has same # protons and electrons.

The Nuclear Atom: protons Nucleus neutrons + - electrons - +

Subatomic Particles: Charge? Location? neutrons (n) protons (p) electrons (e)

Subatomic Particles: Charge? Location? neutron 0 nucleus proton -1 outside neutron proton electron Charge? Location?

Subatomic Particles: Mass (amu) 1  0 (1/1837) neutron proton electron

Elements Each element has a unique number of protons in its nucleus Number of protons in the nucleus of an atom is called the atomic number the elements are arranged on the Periodic Table in order of their atomic numbers Each element has a unique name and symbol symbol either one or two letters one capital letter or one capital letter + one lower case

How many? protons = depends on element neutrons = variable for each element electrons = same as protons

atomic number - The number of protons in one atom; each element has a different atomic number The number on top of the element symbol in the periodic table

The Periodic Table of Elements

Review What is the atomic number of boron, B? What is the atomic mass of silicon, Si? How many protons does a chlorine atom have? How many electrons does a neutral neon atom have? Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral? Will an atom with 27 protons, 32 neutrons and 27 electrons be electrically neutral? Will a Na atom with 10 electrons be electrically neutral?

Review What is the atomic number of boron, B? 5 What is the atomic mass of silicon, Si? 28.09 amu How many protons does a chlorine atom have? 17 How many electrons does a neutral neon atom have? 10 Will an atom with 6 protons, 6 neutrons and 6 electrons be electrically neutral? Yes Will an atom with 27 protons, 32 neutrons and 27 electrons be electrically neutral? Yes Will a Na atom with 10 electrons be electrically neutral? No

Three Types of Elements = Metal = Metalloid = Nonmetal

Metals Solids at room temperature, except Hg Shiny Conduct heat, electricity Malleable: can be shaped Ductile = drawn or pulled into wires Lose electrons and form cations (+ charge) in reactions About 75% of the elements are metals

Nonmetals Found in all 3 states Poor conductors of heat & electricity Solids are brittle Gain electrons in reactions to become anions (- charge) Only a few on the right of periodic table

does not conduct heat well Metalloids Show some properties of metals and some of nonmetals Also known as semiconductors Properties of Silicon shiny conducts electricity does not conduct heat well brittle

The Modern Periodic Table Elements with similar chemical and physical properties are in same column Columns are called Groups or Families designated by a number and letter at top Rows are called Periods Each period shows the pattern of properties repeated in the next period

The Modern Periodic Table Main Group = Representative Elements = ‘A’ groups Transition Elements = ‘B’ groups all metals Bottom rows = Inner Transition Elements = Rare Earth Elements metals really belong in Period 6 & 7

= Alkaline Earth Metals = Alkali Metals = Alkaline Earth Metals = Noble Gases = Halogens = Lanthanides = Actinides = Transition Metals add pictures of elements from text

Important Groups - Hydrogen nonmetal colorless, diatomic gas very low melting point & density reacts with nonmetals to form molecular compounds HCl is acidic gas H2O is a liquid reacts with metals to form hydrides metal hydrides react with water to form H2 HX dissolves in water to form acids

Important Groups – IA, Alkali Metals hydrogen usually placed here, though it doesn’t belong soft, low melting points,low density very reactive, never find uncombined in nature tend to form water soluble compounds react with water to form basic (alkaline) solutions and H2 releasing a lot of heat lithium sodium potassium rubidium cesium

Important Groups – IIA, Alkali Earth Metals harder, higher melting, and denser than alkali metals reactive, but less than corresponding alkali metal form stable, insoluble oxides from which they are normally extracted oxides are basic = alkaline earth beryllium magnesium calcium strontium barium

Important Groups – VIIA, Halogens nonmetals F2 & Cl2 gases; Br2 liquid; I2 solid all diatomic very reactive react with metals to form ionic compounds HX all strong acids except HF fluorine chlorine bromine iodine

Important Groups – VIIIA, Noble Gases all gases at room temperature, very low melting and boiling points very unreactive, practically inert very hard to remove electron from or give an electron to

Charged Atoms = Ions Number of protons (atomic #) identifies the element! all sodium atoms have 11 protons in the nucleus In chemical change, number of protons in nucleus of atom doesn’t change! Atoms can lose or gain electrons becoming electrically charged, these are called ions

Ions Atoms acquire a charge by gaining or losing electrons not protons!! Ion Charge = # protons – # electrons ions with a + charge are called cations more protons than electrons form by losing electrons ions with a – charge are called anions more electrons than protons form by gaining electrons

Atomic Structures of Ions Metals form cations For each positive charge the ion has 1 less electron than the neutral atom Na atom = 11 p+ and 11 e-, Na+ ion = 11 p+ and 10 e- Ca atom = 20 p+ and 20 e-, Ca2+ ion = 20 p+ and 18 e- Cations are named the same as the metal sodium Na  Na+ + 1e- sodium ion calcium Ca  Ca2+ + 2e- calcium ion The charge on a cation can be determined from the Group number on the Periodic Table Group 1A  +1, Group 2A  +2, (Al, Ga, In)  +3

Atomic Structures of Ions Nonmetals form anions For each negative charge the ion has 1 more electron than the neutral atom F = 9 e-, F- = 10 e- P = 15 e-, P3- = 18 e- Anions are named by changing the ending of the name to -ide fluorine F + 1e-  F- fluoride ion oxygen O + 2e-  O-2 oxide ion Charge on an anion can be determined by subtracting 8 from the Group number on the Periodic Table Group 7A  7- 8 = -1; Group 6A  6 – 8 = -2

Example: Find the number of protons and electrons in the Ca2+ ion.

Find the number of protons, electrons, & neutrons or the chagre in the following ions: Na+, O2- , Cl 17 protons & 18 electrons, Nitrogen 7 protons & 10 electrons

Ion Charge & the Periodic Table Charge on an ion can often be determined from an element’s position on the Periodic Table Metals are always positive ions, nonmetals are negative ions For many main group metals, the charge = the group number For nonmetals, the charge = the group number - 8

Charges of Main Group Ions IA VIA IIA IIIA VA VIIA Li+1 Be+2 N-3 O-2 F-1 Na+1 Mg+2 Al+3 P-3 S-2 Cl-1 K+1 Ca+2 Ga+3 As-3 Se-2 Br-1 Rb+1 Sr+2 In+3 Te-2 I-1 Cs+1 Ba+2

Mass # Atomic # C. Isotopes Isotope symbol: “Carbon-12” Atoms of the same element with different numbers of neutrons. Isotope symbol: Mass # Atomic # “Carbon-12”

Isotopes Isotopes = atoms of an element that have same # of protons but different # of neutrons Isotopes of an element have different masses isotopes are identified by their mass numbers = protons + neutrons All isotopes of an element are chemically identical undergo the exact same chemical reactions

Isotope Symbols Cl-35 makes up about 75% of chlorine atoms in nature, and Cl-37 makes up the remaining 25% Average atomic mass of Cl = 35.45 amu Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17) Cl 35 17 or Cl-35 X = Atomic Symbol A = mass number Z = atomic number AX Z

Example: How many protons and neutrons in the chromium isotope

C. Isotopes © Addison-Wesley Publishing Company, Inc.

C. Isotopes Average Atomic Mass reported on Periodic Table weighted average of all isotopes Or multiply the relative abundance (%) by the mass of that isotope. Avg. Atomic Mass

C. Isotopes EX: About 8 out of 10 chlorine atoms are chlorine-35. Two out of 10 are chlorine-37. Avg. Atomic Mass 35.4 u

Neon 9.25% 22 12 10 Ne-22 0.27% 21 11 Ne-21 90.48% 20 Ne-20 Symbol Percent Natural Abundance Mass Number Number of Neutrons Number of Protons Symbol