chapter 2 atoms chemistry b11. matter anything that occupies space and has mass pure substances...

Chapter 2

Atoms

Chemistry B11

MatterAnything that occupies

space and has mass

Pure substancesFixed composition, cannot

be more purified

MixturesA combination of two

or more pure substances

PhysicallySeparable into

ElementCannot be

subdivided by chemical or

physical means

CompoundsElements united

In fixed ratios

HomogeneousmatterUniform

Compositionthroughout

Heterogeneousmatter

Nonuniformcomposition

CombineChemically

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.

H2O (Water): 2 Hydrogen & 1 Oxygen

CO2: 1 Carbon & 2 Oxygen

20 million compounds

Compounds Formula

Identifies each element Ratios

H2O

CO

H

O

2=

1or 2 : 1

C

O

1=

1or 1 : 1

O

H HH2O

Molecularformula

Structuralformula

Ball-and-stickmodel

Space-fillingmodel

Molecular models

C

H

H

H

HCH4

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

N2 O2

Polyatomic

Element:

S8

Atom

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

Atom

Mass number (A): Protons + Neutrons

Atomic number (Z): Protons

C12

6

Mass number

Atomic number

Isotopes

Isotopes: atoms with the same number of protons and electrons butdifferent numbers of neutrons.

different mass numbers

C12

6 C13

6 C14

6

6 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 Cl35

17Cl37

1734.97 amu 36.97 amu

(75.77/100 × 34.97 amu) + (24.23/100 × 36.97 amu) = 35.45 amu

Cl17

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: same properties (main group)

Row or Period

Group 1A: Alkali metals

Li-Na-K-Rb-Cs-Frtoo reactive, unstable, solid metal

2Na + 2H2O 2NaOH + H2

2Na + Cl2 2NaCl

Group 2A: Alkaline metals or Earth metals

Be-Mg-Ca-Sr-Ba-Rareactive, solid metal

Group 7A: Halogens

F-Cl-Br-I-Atreactive, colored, gas, nonmetal

Group 8A: Noble gases

He-Ne-Ar-Kr-Xe-Rnnon 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

to

More metallic

Mo

re m

etal

lic

Metallic properties

n=1

n=2n=3 n=4

n=5

E1 E2 E3 E4 E5

E1 = ground state: lowest energy level

Bohr model

Principal energy levels or Shells

324

183

82

21

Maximum number of electrons

Shell

Lower energy

Higher energy

Subshell: s p d f

Orbital: is a region of space and it can hold 2 electrons (max).

s px py pz

magnetic field

paired spins

s p d f

2 2+2+2=6 2+2+2+2+2=10 2+2+2+2+2+2+2=14

Subshell: s p d f

Shell OrbitalsMaximum number of electrons

1 1s 2

2 2s, 2p 2 + 6 = 8

3 3s, 3p, 3d 2 + 6 + 10 = 18

4 4s, 4p, 4d, 4f 2 + 6 + 10 +14 = 32

3

2

3d3p

3s2p

2s

Principal energy level Orbitals

En

erg

y

Ord

er

of

filli

ng

1 1s

Electrons configuration: description of the orbitals that its electrons occupy.

Orbital box diagrams

H (1)1s

1s1

Electron configuration

1sHe (2) 1s2

Li (3)

1s 2s

1s2 2s1

C (6)

1s 2s

1s2 2s2 2p2

2px 2py 2pz

Noble gas notation

Li (3)1s 2s

1s2 2s1

[He] 2s1

F (9)1s 2s

1s2 2s2 2p5

[He] 2s2 2p52px 2py 2pz

Si (14)1s 2s 3s2px 2py 2pz 3px 3py 3pz

1s2 2s2 2p6 3s2 3p2

[Ne] 3s2 3p2

Valence electrons: outer-shell electrons

Valence shell: outer shell

Cl (17) 1s2 2s2 2p6 3s2 3p5 7 valence electrons

Ar (18) 1s2 2s2 2p6 3s2 3p6 8 valence electrons

C (6) 1s2 2s2 2p2 4 valence electrons

Ne (10) 1s2 2s2 2p6 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

Ion

izat

ion

en

erg

y