unit 5 the periodic table the how and why. newlands -1865 u arranged known elements according to...
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Unit 5The Periodic Table
The how and whyThe how and why
Newlands -1865 Arranged known elements
according to properties & order of increasing atomic mass
Law of Octaves – pattern of chemical & physical properties repeated every 8 elements
Mendeleev - 1869 Created 1st periodic table (63 elements) Ordered by increasing atomic mass Predicted pattern of missing elements Started new rows and lined up
columns to organize elements with similar properties
Rearranged elements so similar properties would line up correctly
The Modern Table Moseley- determined the atomic
number for each known element. Elements are still grouped by properties Similar properties are in the same
column Ordered by increasing atomic number Added a column of elements Mendeleev
didn’t know about – noble gases
Periodic Law When elements are arranged in
order of increasing atomic number, elements with similar properties appear at regular intervals
Horizontal rows are called periods There are 7 periods
Vertical columns are called groups. Elements are placed in columns by
similar properties.
Also called families
1A 2A
3A 4A 5A 6A 7A
8A
3B 4B 5B 6B 7B 8B 8B 8B 1B 2B
1 2
13 14 15 16 17
18
3 4 5 6 7 8 9 10 11 12
IA IIA
IIIB
IVB
VB
VIB
VII
B
VII
IB
IIIA
IVA
VA
VIA
VII
A
VII
IA
IB IIB
Other Systems
1A
2A 3A 4A 5A 6A7A
8A0
The elements in the A groups are called the representative elements
Transition metals The Group B
elements
These are called the inner transition elements and they belong here
Three Classes of ElementsMetalsNonmetalsMetalloids
Metals
Metals Ductile – drawn into wires Malleable – hammered into sheets All solid at room temperature (except
Hg- Mercury) Conductors of heat and electricity Families
– 1 - Alkali– 2 - Alkaline Earth– Transition (B groups)
Group 1A are the alkali metals VERY reactive because one valence e-
• Found as compounds in nature• Not including H!
Group 2A are the alkaline earth metals Still highly reactive but not as much so
as alkali metals (2 valence e-)
Transition Metals The weird ones… May lose different #s of valence
electrons depending on the element with which it reacts
Less reactive than alkali or alkaline earth metals
Good conductors of electricity & heat, ductile, malleable
Inner Transition Metals 1st row = lanthanides
• Shiny metals similar in reactivity to alkaline earth metals
2nd row = actinides
• Unstable nuclei – all radioactive
Non-metals
Non-metals Most are gases, some solid, and 1
liquid (Br) More variation than metals Families
–Halogens (Group 17 or 7A)–Noble Gases (Group 18 or 8A)
Group 7A is called the Halogens Most reactive non-metals – 7 valence
React frequently with alkali metals
Group 8A are the noble gases
Low reactivity, very stable, inert
Metalloids or Semimetals
Metalloids Border the staircase between
metals and nonmetals Properties – similar to metals and
nonmetals
Part 2Periodic trends
Identifying the patterns
What we will investigate Atomic size
• how big the atoms are Ionization energy
• How much energy to remove an electron
Electronegativity
• The attraction for the electron in a compound
What we will look for Periodic trends
• How those things vary as you go across a period
Group trends
• How those things vary as you go down a group
Why?
• Explain why these variations exist
Atomic Size Where do you start measuring? The electron cloud doesn’t have a
definite edge. Scientists focused first on diatomic
elements -- measured more than 1 atom at a time
Atomic Size
Atomic Radius = half the distance between two nuclei of molecule
}Radius
Atomic Size - Periodic Trends The positive nucleus pulls on electrons Periodic trend
• As you move across a period, elements have more protons
• The charge on the nucleus gets bigger
• The outermost electrons of each element are in the same energy level
• So there is more pull on the outermost electrons as you move across
Periodic Trends As you go across a period, the radius
gets smaller. Same outermost energy level More nuclear charge Pulls outermost electrons closer
Na Mg Al Si P S Cl Ar
Atomic Size – Group Trends The positive nucleus pulls on electrons Group Trend
• As you go down a group, you add energy levels
• Outermost electrons not as attracted by the nucleus
+
Shielding Increasing numbers of
electrons between the nucleus and the valence electrons tends to decrease the force between the nucleus & the valence electrons
+
Shielding The electron on the
outside energy level has to look through all the other energy levels to see the nucleus
Shielding The electron on the
outside energy level has to look through all the other energy levels to see the nucleus
A second electron has the same shielding
In the same energy level (period) shielding is the same
+
Shielding As the energy levels
changes the shielding changes
Moving down the group
• More energy levels
• More shielding
• Outer electron less attracted
+
No shieldingOne shieldTwo shieldsThree shields
Group trends As we go down a
group
• Each atom has another energy level
• More shielding
• The atoms get bigger
HLi
Na
K
Rb
Overall
Atomic Number
Ato
mic
Rad
ius
(nm
)
H
Li
Ne
Ar
10
Na
K
Kr
Rb
Atomic size increases,
IONIZATION ENERGY
It’s all about stability Alkali metals are more stable if
they lose an electron Example
• Sodium ([Ne] 3s1)
• Getting rid of the 3s1 electron makes sodium more stable and creates a sodium ion (Na1+)
Ionization Energy The amount of energy
required to completely remove an electron from a neutral atom.
The energy required for the 1st electron is called the first ionization energy
Ionization Energy The 2nd ionization energy is the
energy required to remove the second electron
Always greater than 1st IE The 3rd IE is the energy required to
remove a third electron Greater than 1st or 2nd IE
Symbol First Second ThirdHHeLiBeBCNO F Ne
1312 2731 520 900 800 1086 1402 1314 1681 2080
5247 7297 1757 2430 2352 2857 3391 3375 3963
1181014840 3569 4619 4577 5301 6045 6276
Group trends As you go down a group first IE
decreases
• Valence e- farther from nucleus
• More shielding
Periodic trends First IE increases from left to right
across a period
• Increased nuclear charge from added proton
• Electron shielding not an issue b/c valence are all in same energy level
Exceptions at full and 1/2 full orbitals
• Lower IE b/c offer stability to atom
Ionization energy
INCREASE
How to remember?HILO
LO
Firs
t Ion
izat
ion
ener
gy
Atomic number
He
He has a greater IE than H
same shielding greater nuclear
charge
H
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Li has lower IE than H
more shielding outweighs greater
nuclear charge
Li
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Be has higher IE than Li
same shielding greater nuclear
charge
Li
Be
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He B has lower IE than Be same shielding greater nuclear charge By removing an
electron we make s orbital full
Li
Be
B
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Li
Be
B
C
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Li
Be
B
C
N
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Li
Be
B
C
N
O
Breaks the pattern because removing an electron gets to 1/2 filled p orbital
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Li
Be
B
C
N
O
F
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Li
Be
B
C
N
O
F
Ne Ne has a lower
IE than He Both are full, Ne has more
shielding
Firs
t Ion
izat
ion
ener
gy
Atomic number
H
He
Li
Be
B
C
N
O
F
Ne Na has a lower
IE than Li Both are s1
Na has more shielding
Na
Firs
t Ion
izat
ion
ener
gy
Atomic number
Electronegativity
Electronegativity There’s an electron tug of war
between atoms in a compound The tendency for an atom to attract
electrons to itself when it is chemically combined with another element
How “greedy” Large electronegativity means the
atom pulls the electron towards itself
Group Trend As you move down a group
• More shielding
• Less attraction for electrons
• Lower electronegativity
Periodic Trend As you move across a period
from left to right,
• Nuclear charge increases
• Greater electronegativity
Electronegativity
INCREASE
How to remember?HILO
LO
All 3 trendsHILO
LO
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