Chemical Foundations: Elements, Atoms, and Ions Chemistry 101 Chapter 4 Chemical Foundations: Elements, Atoms, and Ions

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.

Element abundance on earth Ti: 0.6% Others: 0.9% O - O O2 Almost half of the mass is oxygen. 20% of atmosphere.

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

Dalton’s Atomic theory All matter is made up of very tiny, indivisible particles (atoms). All atoms of a given element have the same chemical properties. 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 or 2 : 1 C 1 : 1 H2O CO

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

H2O Chemical Formula Compound Formula Identifies each element Ratios Subscript (number of each atom) Subscript 1 is not written.

H2O CH4 Molecular models O H H C Molecular formula Structural Ball-and-stick model Space-filling C H CH4

Atom + - (Source of  particles)

Atom Nucleus: positive charge Atoms are neutral.                                                                                        Atoms are neutral.                                                                                        Atomic mass unit (amu) = 1.6605×10-24 g mass of proton = 1 amu mass of neutron = 1 amu mass of electron = 5.48×10-4 amu

C Atom Mass number: Protons + Neutrons Atomic number: Protons 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 14 6 6 P + 6 N 6 P + 7 N 6 P + 8 N Carbon-12 Carbon-13 Carbon-14 Almost the same properties

Cl Cl Atomic Weight Cl Cl Atomic weight: of an element is average of the masses (in amu) of its isotopes found on the Earth. Cl 35 37 Cl Cl 34.97 amu 36.97 amu 17 17 (75.77/100 × 34.97 amu) + (24.23/100 × 36.97 amu) = 35.45 amu Cl 17 35.45 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 (7 rows)

too reactive, unstable, solid metal Group 1A: Alkali metals Li-Na-K-Rb-Cs-Fr too reactive, unstable, solid metal 2Na + 2H2O 2NaOH + H2 2Na + Cl2 2NaCl Group 2A: Alkaline metals or earth metals Be-Mg-Ca-Sr-Ba-Ra reactive, solid metal

reactive, colored, gas, nonmetal 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

Classification of the elements metals nonmetals metalloids 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

They occur in compounds. Most elements are reactive and they cannot be found in nature in free form. They occur in compounds. Noble metals: unrecative metals Ag, Au, Pt Monatomic Ar He Diatomic N2 O2 Polyatomic S8 Noble gases

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

Metallic properties More metallic More metallic

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

Na+ Na Ions & Ionization + e- Na + energy → Na+ + e- ion 11+ 11- 10- The size of the cation is smaller than the neutral atom.

Ions & Ionization Cl + e- → Cl- ion Cl- + e- Cl 17- 18- 17+

Ionization Energy 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+) Ions Nonmetals: gain 1, 2 or 3 e- Anion (X-) Transition elements 1A 2A 3A 4A 5A 6A 7A 8A

Ionic Compounds Ionic compounds are salts containing cations and anions. The positive charge of the cation(s) must balance the negative charge of the anion(s) to form a neutral compound.

Ionic Compounds Sometimes several cations balance one anion. Sometimes one cation needs several anions.

Ionic Compounds Mg → Mg2+ + 2e- Cation Cl + e- → Cl- Anion Mg2+ 2Cl-

Ionic Compounds Li → Li+ + e- Cation S + 2e- → S2- Anion 2Li+ S2- Li2S Al → Al3+ + 3e- Cation O + 2e- → O2- Anion 2Al3+ 3O2- Al2O3

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