electrons and atoms

8/11/2019 Electrons and atoms

1/44

Atoms

Atomic number, mass number, and isotope

Periodic Table Molecules and Ions

Chemical Formula

Nomenclature

Atoms, Molecules, and Ions


2/44

I. Atoms A. Daltons atomic theory

Elements are made of atoms

Compounds are composed of atoms of more than oneelement in fixed ratio

Chemical reaction involves rearrangement of atoms

2


3/44

8 X 2Y16 X 8 Y+

Chemical reaction involves rearrangement of atoms


4/44

2 H 2

Chemical Reactions

=

= 2 H 2O

+

+ O 2


5/44

J.J. Thomson, measured mass/charge of e -

(1906 Nobel Prize in Physics)

Cathode ray experiment

B. Structure of an atom


6/44

Cathode Ray Tube


7/44

e - charge = -1.60 x 10 -19 C

Thomsons charge/mass of e - = -1.76 x 10 8 C/g

e- mass = 9.10 x 10

-28 g

Measured mass of e -

(1923 Nobel Prize in Physics)

Oil drop experiment


8/44

1. atoms positive charge is concentrated in the nucleus2. proton (p) has opposite charge

3. mass of p is 1840 x mass of e-

(1.67 x 10-24

g)


9/44

B. Structure of an atom

atomic radius ~ 100 pm = 1 x 10 -10 m

nuclear radius ~ 5 x 10 -3 pm = 5 x 10 -15 m

Rutherfords Model of the Atom


10/44

mass p mass n 1840 x mass e -


11/44

B. Structure of an atom An atom contains protons , electrons , and neutrons

An atom is neutral

no. of p = no. of e

Almost all the mass of atom comes from the protons andneutrons

A He atom


12/44

II. Atomic Number and Isotopes

Atomic number (Z)

Number of protons in the nucleus Identifies the atom

ex: Z=7, ; for K, Z= .

Mass number (A) number of protons + number of neutrons(n)

A = Z+ n

Z

Aelementsymbol

Isotopes

Elements have the same number of protons (Z) butdifferent number of neutrons (n or A)

ex: 126C 146C


13/44

Isotopes of Hydrogen

H11 H (D)21 H (T)

31


14/44

Exercise

Element 11C 75As

No. of p 24

No. of e

No. of n

Mass number (A)

28


15/44

Period Gr o

u p

A l k

al i M e

t al

N o b l e

G a s

H al o g

en

A l k al i E

ar t h

M e t al


16/44

III. The Periodic Table - Organization of Elements

Vertical Columns: groups or families , elements have similar properties

Alkali Metals (1A): Li, Na, K, Rb, Cs, Fr

Alkaline Earth Metals (2A): Be, Mg, Ca, Sr, Ba, Ra

Halogens (7A): F, Cl, Br, I, At

Noble Gas (8A): He, Ne, Ar, Kr, Xe, Rn

Horizontal Rows: periods

Arranged by atomic number

Q: Which pair of elements would you expect to exhibit the greatestsimilarity in their physical and chemical properties?(1) P and S (2) Cs and Co(3) Mg and Ca (4) H and He


17/44

III. The Periodic Table - Organization of Elements

Metal, Metalloids, and Nonmetals Metals : good conductors of heat/electricity Nonmetals : poor conductors of heat/electricity Metalloids Metal characters increases

(1) down group and (2) from right to left across a period Physical state of elements at room temperature

Most are solids 2 are liquids : Br 2, Hg

11 gases: H 2, N 2, O 2, F 2, Cl 2, He, Ne, Ar, Kr, Xe, Rn

Q: Which of the following elements is most likely to be a poorconductor of electricity?

(1) Na (2) Cu (3) Os (4) Ne


18/44

H2 H2O NH 3 CH 4

IV. Molecules and Ions Molecules :

groups of atoms jointed together by chemical bonds in a

definite arrangement electrically neutral

Molecular Compounds

has molecules as units when atoms of nonmetals combine to form compound

Diatomic molecule (2 atoms)/Polyatomic moleculeH2, N 2, HCl, HBr O 3, H 2O, CO 2


19/44

Exercise

Unit

Atom or

molecule?

Element or

compound?

Number of atoms

of each element

F2

Ne

HCN

CHBr 3


20/44

Ions When atoms or molecules gain or lose electrons

Cations : positively charged ions (lose electrons)

Ca > Ca 2+ + 2 e

Anions : negatively charged ions (gain electrons)

Cl + e

> Cl

Ca 20 protons

20 electrons

Ca 2+ protons

electrons

Cl17 protons

17 electronsCl -

protons

electrons


21/44

Q: How many protons, electrons and neutrons are in ?Al27133+

Q: How many protons, electrons, and neutrons are in ?Se78 2-

Q: Which is a cation that has 10 electrons?(1) Ne (2) Mg 2+ (3) F - (4) Na -


22/44

Ions

A monatomic ion contains only one atom

Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3-

A polyatomic ion contains more than one atom

OH -, CN -, NH 4+, NO 3-

Metal tends to form cations

K +, Cu 2+, Mg 2+, NH 4+

Nonmetal tends to form anions

S2-, O 2-, N 3-, F -, NO 3-, CN -

Ionic compounds - composed of ions, NaCl, KF


23/44

Common Ions Shown on the Periodic Table


24/44

V. Chemical Formulas

Chemical formula : use symbols to represent molecules/ions

ex. H 2O, CO 2, NO 3 , NH 4+, IF 3

Subscript indicates the number of atoms in the molecule

The element to the left of periodic table is usually written on theleft side of the formula, HCl, CO 2 (exception : NH 3, CH 4 )

The lower element in the same group is usually written first, IF 5,BrCl

M olecular f ormula

Shows the actual number of each type of atom in a molecule.

Allotrope : one or more distinct forms of an element, O 2 and O 3

Structural formula

Show how the atoms are connected in molecules/ions


25/44

Formulas and Models


26/44

V. Chemical Formulas

Empirical Formula

The simplest formula that shows the ratios of the number ofatoms of each element in a compound

Molecular formula are multiples of the empirical formula.

M olecular F ormula Empir ical F ormula

H2O2

H2O

C6H6C4H10


27/44

V. Chemical Formula

Formula of ionic compounds Empirical formula Find the charges on the cations and anions, cancel the charge using

minimum # of cations and anions (sum of all charges must be zero)

Enclose polyatomic ions in ( ) if more than one is used

The ionic compound NaCl

MgCl 2

1 x 2 = +2 2 x (-1) = -2

Mg 2+ Cl - Al2(SO 4)3

2 x 3 = +6 3 x (-2) = -6

Al 3+ SO 42-


28/44

The most reactive metals (green) and the most reactive nonmetals (blue)combine to form ionic compounds.


29/44

Q: Predict the empirical formula of the ionic compound thatforms from (a) Al and O, (b) Ca and F, (c) Na and CO 32-

(a) Al and O

(b) Ca and F

(c) Na and CO 32-


30/44

VI. Chemical Nomenclature Ionic compounds

Generally made of metal (cations) + nonmetal (anions), ex: NaCl, KF

Name metal first, then anion Cations , use element name

Only one cation possible: group 1A, 2A, Al, Ag, Zn More than one cation possible: other metals, use Roman numerals to

indicate charge on metal ion Anions

Monatomic anion: changing the end of the element name by ide

Polyatomic anion: ending with -ate, -ite, or ide

BaCl 2

K 2O

Mg(OH) 2

CuNO 3

SnO2 SnO


31/44

Transition metal ionic compounds

indicate charge on metal with Roman numerals

FeCl 2

FeCl 3

Cr 2S3

Few more examples


32/44

Monatomic anions


33/44


34/44

VI. Chemical Nomenclature

Molecular compounds

Generally made of nonmetals or nonmetals + metalloids Name the element to the left of periodic table first

Name the lower element in the same group first

If more than one compound can be formed

from the same elements, use Greek prefixes

to indicate the number of each atom

last element ends in -ide

Q: Which one of the following is both a moleculeand a compound?(1) P 4 (2) CaF 2 (3) CO 2 (4) He

Ch i l l l l C d


35/44

HI

NF 3

SO 2

dinitrogen tetrachloridenitrogen dioxide

dinitrogen monoxide

VI. Chemical Nomenclature Molecular Compounds

Q: Identify the following compounds as molecular (M) or ionic (I).

CCl 4 Mg 3 N 2(NH 4)2CO 3 IF 5


36/44


37/44

VI. Chemical Nomenclature Acid Acid

Yields H + when dissolved in water

For example: HCl gas and HCl in water

Pure substance, hydrogen chloride

Dissolved in water (H 3O+ and Cl ),

hydrochloric acid

VI Chemical Nomenclature Acid


38/44


Acid from anion ending with -ide, add prefix hydro and

replace -ide with -ic acidHBr (pure substance)

HBr (dissolved in water)

VI Chemical Nomenclature Acid


39/44


Oxoacid: acid that contains hydrogen, oxygen, and another

element

HNO 3 nitric acid

H2CO 3 carbonic acid

H3PO 4 phosphoric acid

VI Ch i l N l t A id


40/44

VI. Chemical Nomenclature Acid Oxoacid: acid that contains H, O, and another element

When all the H ions are removed from the -ic acid, the

anions name ends with -ate.

When all the H ions are removed from the -ous acid, theanions name ends with -ite.

The names of anions in which one or more but not all the

hydrogen ions have been removed must indicate the number ofH ions present.

HNO 3:

H2SO 3:H2SO 4:

NO 3-:

SO 32-:SO 42-:

H2PO 4-:

HPO 42-

:

PO 43-:

H3PO 4:

Naming Oxoacids and Oxoanions


41/44

g


42/44

VI. Chemical Nomenclature Acid

HBrO 4:

HBrO 3:HBrO 2:

HBrO:

IO 4- :

IO 3-

:IO 2- :

IO - :


43/44

VI. Chemical Nomenclature Base and hydrate

Base:

Yields OH when dissolved in water

Example : KOH

Ba(OH) 2

Fe(OH) 3 Hydrate

Compound that have a specific number of water attached to it

CuSO 4.5H 2O

MgSO 4.7H 2O

Sr(NO 3)2 4H 2O


44/44

More practice!

carbon dioxide potassium sulfite

diphosphorus pentoxide sodium chloride

lithium oxide perbromic acid

magnesium phosphide copper (II) sulfate

FeS CoCl 3

N 2O OCl 2

Ca(NO 3)2 (NH 4)2CO 3

Sn(ClO 2)4 Pb 3 N2

electrons and atoms

Documents