Download 2- Periodic Trends

Periodic Table
Trends
Mendeleev (1870)
• Russian scientist and professor
• Arranged the 63 elements by atomic mass
• Noticed a repetition of properties (periodicity)
• Called the pattern of properties “Periodic Law”
Mendeleev (correctly) predicted the mass of elements yet to
be discovered and left spaces open for them
Moseley (1913)
Experiments showed proton number was a better method to
organize the elements.
• Repetition of properties (periodicity) became more clear
Modern Periodic Law:
“The properties of elements are a periodic function of
increasing atomic number”
We know now that most element properties
are due to the number of valence electrons
An updated Periodic Table containing ALL 118 elements – separated into
metal and non-metal atoms make up EVERYTHING in the Universe.
Rows of the periodic table are called periods.
• Elements in periods do not have similar properties
Non-metal
Element with
properties opposite
to those of metals
(brittle, dull…)
periods
Left to right
Elements change from metals to non-metals
Columns of the periodic table are called groups.
•Elements in groups have similar properties
A family is a group with a specific name:
Family names and locations need to be memorized
GROUP
•
•
•
•
•
Alkali metals
Alkaline Earth metals
Chalogens
Halogens
Noble (inert) gases
Transition Metals: groups 3 – 12
• unique properties different from group 1 and 2 metals
(make coloured compounds, speed up chemical reactions…)
Hydrogen*
• Group 1
• Non-metal gas
• 1 valence electron
• Simplest atomic structure - only 1 e- and 1 p+
• Highly chemically reactive
The placement of
hydrogen is only
because of its
structure - 1
proton…
Sometimes a table
will have it raised
above the Alkali
Metals to avoid
confusion
Increasing Reactivity
The LESS electrons needed, the GREATER the chemical
reactivity of the element
CAN YOU ANSWER THESE QUESTIONS?
S1-2-06
How is the Periodic Table organized for the elements and what
trends exist?
Vocabulary & Concepts
Mendeleev
Period
Family
Alkali metals
Transition Metals Chalcogens
Noble gases
Group
Earth metals
Halogens
IONS
• IONS are atoms or groups of atoms with a positive or negative
charge.
• Taking away an electron from an atom gives a CATION with a
positive charge
• Adding an electron to an atom gives an ANION with a
negative charge.
• To tell the difference between an atom and an ion, look to see if
there is a charge in the superscript! Examples: Na+ Ca+2 I- O-2
Na Ca I
O
Forming Cations & Anions
A CATION forms
when an atom
loses one or more
electrons.
Mg --> Mg2+ + 2 e-
An ANION forms
when an atom
gains one or more
electrons
F + e- --> F-
PREDICTING ION CHARGES
In general
• metals (Mg) lose electrons ---> cations
• nonmetals (F) gain electrons ---> anions
Learning Check – Counting
State the number of protons, neutrons, and electrons in
each of these ions.
39
K+
19
16O -2
41Ca +2
8
20
#p+ ______
______
_______
#no ______
______
_______
#e- ______
______
_______
One Last Learning Check
Write the nuclear symbol form for the following
atoms or ions:
A. 8 p+, 8 n, 8 e-
___________
B. 17p+, 20n, 17e-
___________
C. 47p+, 60 n, 46 e-
___________
Charges on Common Ions
-3
+1
-2
-1
+2
By losing or gaining e-, atom has same number
of e-’s as nearest Group 8A atom.