Chapter 2 Atoms Chemistry B11

Matter Anything that occupies space and has mass Pure substances Fixed composition, cannot be more purified Mixtures A combination of two or more pure substances Physically Separable into Element Cannot be subdivided by chemical or physical means Compounds Elements united In fixed ratios Homogeneous matter Uniform Composition throughout Heterogeneous matter Nonuniform composition Combine Chemically To form

Element: is a substance consists of identical atoms. Cannot be divided by chemical & physical methods. Carbon, Hydrogen, Oxygen 116 elements – 88 in nature Compound: is a pure substance made up of two or more elements in a fixed ratio by mass. H 2 O (Water): 2 Hydrogen & 1 Oxygen CO 2 : 1 Carbon & 2 Oxygen 20 million compounds

Compounds Formula Identifies each elementRatios H2OH2O CO H O 2 = 1 or 2 : 1 C O 1 = 1 or 1 : 1

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

Mixture: is a combination of two or more pure substances. Homogeneous: uniform & throughout Air, Salt in water Heterogeneous: nonuniform Soup, Milk, Blood Mixtures

Law of conservation of mass: C+O  CO 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 formed by the chemical combination of two or more different kinds of atoms. 4. A molecule is a bound combination of two or more atoms. Dalton’s Atomic theory

Monatomic Ar He Diatomic N2N2 O2O2 Polyatomic Element: S8S8 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 (A):Protons + Neutrons Atomic number (Z):Protons C 12 6 Mass number Atomic number

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

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: 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, ductile, malleable nonmetals: solid, liquid or gas, do not conduct electricity (except graphite) metalloids: between metals and nonmetals t o

More metallic Metallic properties

n=1 n=2 n=3 n=4 n=5 E1E1 E2E2 E3E3 E4E4 E5E5 E 1 = ground state: lowest energy level Bohr model Principal energy levels or Shells Maximum number of electrons Shell Lower energy Higher energy

Subshell:spdf Orbital: is a region of space and it can hold 2 electrons (max). spxpx pypy pzpz magnetic field paired spins

s p d f = = =14 Subshell:spdf

ShellOrbitals Maximum number of electrons 11s2 22s, 2p2 + 6 = 8 33s, 3p, 3d = 18 44s, 4p, 4d, 4f = d 3p 3s 2p 2s Principal energy levelOrbitals Energy Order of filling 1 1s

Electrons configuration: description of the orbitals that its electrons occupy. Orbital box diagrams H (1) 1s 1s 1 Electron configuration 1s He (2) 1s 2 Li (3) 1s 2s 1s 2 2s 1 C (6) 1s 2s 1s 2 2s 2 2p 2 2p x 2p y 2p z

Noble gas notation Li (3) 1s 2s 1s 2 2s 1 [He] 2s 1 F (9) 1s 2s 1s 2 2s 2 2p 5 [He] 2s 2 2p 5 2p x 2p y 2p z Si (14) 1s 2s 3s 2p x 2p y 2p z 3p x 3p y 3p z 1s 2 2s 2 2p 6 3s 2 3p 2 [Ne] 3s 2 3p 2

Valence electrons: outer-shell electrons Valence shell: outer shell Cl (17) 1s 2 2s 2 2p 6 3s 2 3p 5 7 valence electrons Ar (18) 1s 2 2s 2 2p 6 3s 2 3p 6 8 valence electrons C (6) 1s 2 2s 2 2p 2 4 valence electrons Ne (10) 1s 2 2s 2 2p 6 8 valence electrons Noble gases Filled valence shells

Elements in the same column (group) have the same number of electrons in their valance shells. The same chemical and physical properties. For Main-group elements:

Lewis dot structure H He Li C Cl 1A 2A 3A 4A 5A 6A 7A 8A

Main groups elements s, p Transition elements s, p, d Inner transition elements s, p, d, f

Atomic Size Size of an atom: is the size of its outermost occupied orbital. d

Ionization Energy Li + energy → Li + + e - ion Ionization energy: the energy required to remove the most loosely held electron from an atom in the gaseous state. Ionization energy