1. Chapter 4 Chemical Foundations: Atoms & Elements Chemistry 100

2. 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 compounds are composed of these 116 elements. Elements & Compounds

3. 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

4. 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

5. 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

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

7. Atom - - - - - - - (Source of  particles) +

8. Atom Nucleus: positive charge 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

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

10. 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 Almost the same properties Carbon-12Carbon-13Carbon-14

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

13. 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)

14. 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

15. 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

16. 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

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

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

19. More metallic Metallic properties

20. 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.

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

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

23. Problem 1 Determine the charge of each ion: a)a magnesium ion with 10 electrons b)A sulfur ion with 18 electrons Ion charge = #P + – #e - a)Magnesium’s atomic number is 12. Ion charge = 12 – 10 = 2+ (Mg 2+ ) b) Sulfur’s atomic number is 16. Ion charge = 16 – 18 = 2- (S 2- )

24. Problem 2 Determine the number of protons and electrons in the Ca 2+ ion: Ion charge = #P + – #e - Calcium’s atomic number is 20. 2+ = 20 – #e - #e - = 20 – 2 = 18

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

26. 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

27. 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.