Transcript chm 115 history of atom perioic table and subatomic particlesx

HISTORY OF THE ATOM
Subatomic particles and the periodic table
Summary of subatomic particles
2
Atoms vs. Elements
3

Blocks analogy
Elements
4

Unique number of protons
 Atomic
number
 Arrangement on periodic table
 Symbol and name
 One
or two letters
 First capital, second lowercase
Chemical Symbols
5
Some symbols are not obvious.
Fe for Iron or Cu for copper,
based on older names
Nucleus
6

Isotopes
 Same
element (same number of protons)
 Different number of neutrons
 Different masses
 Chemically identical
 Mass number= protons + neutrons
Chemical Symbols
7
Practice Writing Symbols
8

What is boron’s atomic symbol if it has 6 neutrons?

What is leads atomic symbol if it has 124 neutrons?
Subatomic Particles Practice
9
Atomic
symbol
Atomic
number
Atomic
Protons
Neutrons
Electrons
11
mass
24
31
37
39
29
89
35
43
100
Ions
10






When compounds are formed, electrons are shared
or given away and taken
Atom that has lost or gained electrons
Protons remain the same, it’s the electrons that are
affecting the charge
Reminder: electrons are negatively charged
Cations: lost electrons, become positive
Anions: gain electrons become negative
Ions and Compounds
11

Ions behave much differently than the neutral atom.
 e.g.,
The metal sodium, made of neutral Na atoms, is
highly reactive and quite unstable. However, the sodium
cations, Na+, found in table salt are very nonreactive
and stable.

Since materials like table salt are neutral, there
must be equal amounts of charge from cations and
anions in them.
Atomic Structures of Ions
12
Nonmetals form anions.
 For each negative charge, the ion has 1 more
electron than the neutral atom.

= 9 p+ and 9 e−, F─ = 9 p+ and 10 e−
 P = 15 p+ and 15 e−, P3─ = 15 p+ and 18 e−
F
Atomic Structures of Ions
13
Metals form cations.
 For each positive charge, the ion has 1 less
electron than the neutral atom.

atom = 11 p+ and 11 e−, Na+ ion = 11 p+ and
10 e−
 Na
atom = 20 p+ and 20 e−, Ca2+ ion = 20 p+ and
18 e−
 Ca
Practice—Complete the Table
Atomic
Number
Protons
16
Electrons
Ion
Charge
Ion
Symbol
18
12
2+
Al3 
36
1−
14
15
Periodic Law
16

Mendeleev
 Ordered
elements by atomic number
 Repeating pattern of properties


Periodic Law—When the elements are arranged in
order of increasing atomic mass, certain sets of
properties recur periodically.
put elements with similar properties in the same
column
Mendeleev’s Periodic Table
17
Mendeleev and Periodic Law
18


used pattern to predict properties of undiscovered
elements
Where atomic mass order did not fit other properties,
he reordered by other properties.

Te & I
Periodic Table
19
Metals
20



Solids, except Hg
Shiny
Conductive
Heat
 Electricity






Malleable
Ductile
Lose electrons, form cations
~75 % of elements
Lower left on table
Nonmetals
21


Solid, liquid and gas
Poor conductors
 Heat
 Electricity


Solids are brittle
Gain electrons
 Anions

Upper right of periodic table, except H
Metalloids
22


Characteristics of both metals and nonmetals
Semiconductors
Modern Periodic Table
23


Elements with similar chemical and physical properties
are in the same column.
Columns are called Groups or Families.



designated by a number and letter at top
Rows are called Periods.
Each period shows the pattern of properties
repeated in the next period.
Modern Periodic Table
24
Main Group = Representative Elements = “A”
groups
 Transition Elements = “B” groups

 all

metals
Bottom Rows = Inner Transition Elements = Rare
Earth Elements
 metals
 really
belong in Periods 6 & 7
Modern Periodic Table
25
Periodic Table Groups
26
Important Groups—Hydrogen
27


nonmetal
colorless, diatomic gas


very low melting point and density
reacts with nonmetals to form molecular compounds
HCl is acidic gas
 H2O is a liquid

Important Groups—Alkali Metals
28





Group 1A = Alkali Metals
hydrogen usually placed here, though it doesn’t really
belong
soft, low melting points, low density
flame tests  Li = red, Na = yellow, K = violet
very reactive, never find uncombined in nature
Important Groups—Alkaline Earth
Metals
29


Group 2A = Alkali Earth Metals
harder, higher melting, and denser than alkali metals
 Mg


alloys used as structural materials
flame tests  Ca = red, Sr = red, Ba = yellow-green
reactive, but less than corresponding alkali metal
Important Groups—Halogens
30
Group 7A = Halogens
 nonmetals
 F2 and Cl2 gases; Br2 liquid; I2 solid
 all diatomic
 very reactive

Important Groups—Noble Gases
31


Group 8A = Noble Gases
all gases at room temperature
 very


low melting and boiling points
very unreactive, practically inert
very hard to remove electron from or give an electron
to
Ion Charge and the Periodic Table
32




The charge on an ion can often be determined from
an element’s position on the Periodic Table.
Metals always form positively charged cations.
For many main group metals, the charge = the
group number.
Nonmetals form negatively charged anions.
Ionic Charges and Periodic Table
33
Practice—What is the charge on each
of the following ions?
34

potassium cation

sulfide anion

calcium cation

bromide anion

aluminum cation