Download Chapter 6 Periodic trends

Chapter 6 Periodic trends
Mendeleev- organized the periodic table by
mass.
 grouped them by similar properties.
- like a game of Solitare.
 didn’t know about subatomic particles at
the time.
 Exception to his rule: Iodine and
tellurium.
- Mendeleev thought that he had
miscalculated the masses since he
knew that iodine belonged in the
group with bromine and chlorine.
 Modern Periodic Table is arranged by
atomic number and grouped by
properties.
 Group numbers are standardized by the
International Union of Pure and Applied
Chemistry (IUPAC)
 There are 3 Classes of elements.
- Metals- conductors, ductile(made
into a wire) and malleable( able to
resist shattering)
- Nonmetals- insulators (except
carbon), brittle, mostly gases
- Metalloids- have properties of both
metals and nonmetals
 Ex. Silicon- alone it is an
insulator (nonmetal)
o Combined with boron it is
a conductor (metal)
Periodic Trends
- Group Trends- what happens within
the group or column of elements
- Period trends – what happens
across a period or row.
 Groups of the periodic table
- “A” elements- Representative
Elements
 1A- Alkali Metals
 2A –Alkaline Earth Metals
 7A – Halogens
 8A – Noble Gases
- “B” Elements are the transition
metals.
- “A” group number corresponds to
the number of valence electrons in
that group.
 Valence Electrons- Outer shell
electrons only
Periodic Trends
Atomic radius
- Measuring an atom- the distance
between two atoms divided by 2
gives the atomic radius.
- 3 factors affect atomic radius
 Energy level- Higher the energy
level the further the electrons are
from the nucleus.
 Charge on the nucleus- more
valence electrons increase
nuclear charge and pull electrons
closer to the nucleus.
 Shielding effect- the ability for
electrons to shield the nucleus
from other electrons.
 Group trend – Atomic radius increases
going down the group.
 Each element in the group has
another energy level
 Atom gets bigger with increased
energy levels
 Period trend- Atomic radius gets
smaller as elements go from left to right
across a period.
- increased nuclear charge pulls
electrons closer to the nucleus.
 Ionization energy(IE)
- Energy required to remove one
electron from a valence shell.
 Remove 1 e- = 1+ ion
- Energy required to remove the 1st
electron is the 1st ionization energy
- Energy required to remove the 2nd
electron is the 2nd ionization energy
 2nd IE is always more than the 1st
IE. 3rd IE is more than the 2nd IE.
- Greater nuclear charge increases IE
because atoms that have fuller
valences are more reluctant to give
up electrons.
- Distance from the nucleus decreases
IE because electrons in upper energy
levels are further away from the
nucleus.
 Group trend- IE decreases
 Period trend -IE increases
Ionic radius – size of an atom once it
becomes and ion
- Cations (metals) lose electrons when
they form ions.
- Anions (Nonmetals) gain electrons
when they form ions.
- As cations lose electrons the ion
radius gets smaller.
- As anions gain electrons they get
bigger.
 Group trend- increases generally
 Period trend- Within cations, ionic
radius decreased from left to right
 Within anions, ionic radius
decreases from left to right.
Electronegativity- the ability of an
atom to attract an electron when
chemically combined with another
element.
- Larger electronegativity will pulls
electrons toward it.
 Group trend – electronegativity
decreases because electrons are further
away from the
nucleus.
 Period trend- electronegativity
increases because there are more
electrons surrounding the nucleus.
 Noble gases are not usually included
in ionic radius and electronegativity
trends because of their lack of
reactivity.
 Summary of trends- pg 178