Chapter 4 Chemical Foundations: Elements, Atoms, and Ions Chemistry B2A

Element: is a substance consists of identical atoms. Cannot be divided by chemical & physical methods. Carbon, Hydrogen, Oxygen 116 elements – 88 in nature Millions of compound are composed of these 116 elements.

H: 0.9% Ti: 0.6% Others: 0.9% Element abundance on earth Almost half of the mass is oxygen. O2O2 20% of atmosphere. O - O

Element Symbols The first letter or two first letters of element name: Oxygen OSilicon Si Carbon C Argon Ar Sometimes, two letters are not the first letters: Chlorine ClZinc Zn Sometimes, old names are used (Latin or Greek): Iron (Ferrum) Fe Lead (Plumbum) Pb

1.All matter is made up of very tiny, indivisible particles (atoms). 2.All atoms of a given element have the same chemical properties. 3.Compounds are made up of two or more different kinds of atoms. A compound has the same relative numbers and types of atoms. Dalton’s Atomic theory Law of constant composition: Compound always has the same composition. Compound always has the same properties. H O 2 = 1 or2 : 1 C O 1 = 1 or 1 : 1 H2OH2O CO

4. Atoms are not created or destroyed in chemical reactions. A chemical reaction changes the way the atoms are grouped together. Dalton’s Atomic theory Law of conservation of mass: C+O  CO

Chemical Formula Compound Formula Identifies each elementRatios H2OH2O Subscript (number of each atom) Subscript 1 is not written.

O H H H2OH2O Molecular formula Structural formula Ball-and-stick model Space-filling model Molecular models C H H H H CH 4

Atom (Source of  particles) +

Atom Nucleus: positive charge Atoms are neutral. Atomic mass unit (amu) = × g mass of proton = 1 amu mass of neutron = 1 amu mass of electron = 5.48×10 -4 amu

Atom Mass number:Protons + Neutrons Atomic number:Protons C 12 6 Mass number (A) Atomic number (Z)

Isotopes Isotopes: atoms with the same number of protons and electrons but different numbers of neutrons. different mass number C 12 6 C 13 6 C P + 6 N 6 P + 7 N 6 P + 8 N Almost the same properties Carbon-12Carbon-13Carbon-14

Atomic Weight Atomic weight: of an element is average of the masses (in amu) of its isotopes found on the Earth. Cl Cl amu amu (75.77/100 × amu) + (24.23/100 × amu) = amu Cl Atomic number Atomic weight

main-group elements: 1A to 8A transition elements: 1B to 8B (3 – 12) inner transition elements: between B3 & B4 (58 to 71 and 90 to 103) Column: the same properties (main group) Row or Period

Group 1A: Alkali metals Li-Na-K-Rb-Cs-Fr too reactive, unstable, solid metal 2Na + 2H 2 O 2NaOH + H 2 2Na + Cl 2 2NaCl Group 2A: Alkaline metals or earth metals Be-Mg-Ca-Sr-Ba-Ra reactive, solid metal

Group 7A: Halogens F-Cl-Br-I-At reactive, colored, gas, nonmetal Group 8A: Noble gases He-Ne-Ar-Kr-Xe-Rn non reactive, stable, gas, nonmetal

nonmetals metals metalloids Classification of the elements Metals: solid (except mercury), shiny, conductors of electricity and heat, ductile, malleable Nonmetals: solid, liquid or gas, do not conduct electricity (except graphite) Metalloids (Semimetals): between metals and nonmetals

Noble metals: unrecative metals Most elements are reactive and they cannot be found in nature in free form. Ag, Au, Pt Monatomic Ar He Diatomic N2N2 O2O2 Polyatomic S8S8 Noble gases

Allotropes Different forms of an element Carbon: Diamond Graphite Buckminsterfullerene & Nanotube

More metallic Metallic properties

Ions Total number of protons = Total number of electrons Atom is neutral (zero net charge). Na → Na + + e - Cl + e - → Cl - Ion: atom with any charges (positive or negative). Cation Anion Number of protons and neutrons in the nucleus remains unchanged.

Na + energy → Na + + e - ion Ions & Ionization Na + + e - Na

Cl + e - → Cl - ion Ions & Ionization Cl - + e - Cl

Ionization energy: the energy required to remove the most loosely held electron from an atom in the gaseous state. Ionization energy Ionization Energy

Metals: lose 1, 2 or 3 e - Cation (Y + ) Nonmetals: gain 1, 2 or 3 e - Anion (X - ) Ions Transition elements 1A2A 3A 4A5A6A7A 8A

Na → Na + + e - Cl + e - → Cl - Cation Anion Ionic Compounds Na + Cl - NaCl Mg → Mg e - Cl + e - → Cl - Cation Anion Mg 2+ 2Cl - MgCl 2

Li → Li + + e - S + 2e - → S 2- Cation Anion Ionic Compounds 2Li + S 2- Li 2 S Al → Al e - O + 2e - → O 2- Cation Anion 2Al 3+ 3O 2- Al 2 O 3