Unit 3, Part 1The Periodic Table

Chemistry Notes

What is Periodicity?

• Means to occur at regular periods/intervals

• In chemistry, it applies to the Periodic Table – the arrangement of elements and their chemical properties

The Periodic Law

• Chemical and physical properties of elements are functions of their ATOMIC NUMBERS

• Periodic means to repeat

• 1st proposed by Dmitri Mendeleev, who related periodic functions to atomic mass

The Periodic Table

• Graphical representation of the Periodic Law

• Elements positioned according to atomic number and electron structure

• Long and short forms

Organization of P.Table

• Group = vertical column• Period = horizontal row

–Elements in the same row have the same number of occupied energy levels.

–So…

Period = Energy Level in Atom

There are 7 periods…

The Zig-Zag Line

• The “Stair case” on the P.Table• Metals – to left • Nonmetals – to right• Metalloids (semi-metals) – along stair case

http://img.sparknotes.com/content/testprep/bookimgs/sat2/chemistry/0001/sat117002_0407.gif

Properties of Metals

• Luster (shiny)

• Conduct heat, electricity

• Malleable (sheets)

• Ductile (wires)• Solid, except for

Mercury (liquid)

• Low numbers of outer (valence) shell electrons

• High density

• Most have high melting points

Nonmetals – have opposite characteristics!

Metalloids

• Often called semi-metals• Properties of both metals & nonmetals• Often used as semi-conductors (Si, Ge)

Alloys

•Mixture of metals

•Changes properties – usually for the better

•Example = brass (Zn, Cu); sterling silver (Ag, Cu)

The Representative Elements

• A elements (main-group)

• Groups 1A – 8A

• Have a wide range of properties

• Elements in the same group (A elements) have the same number of valence electrons, which corresponds to the group number (ex: 6A = 6 valence e-)– Valence Electrons – in outermost energy

level; most likely involved in a chemical reaction

Types of Representative Elements

1A = Alkali Metals

--soft

--very reactive – esp. in water

--found in nature in compound form

--tend to lose 1 electron (form +1 ions)

2A = Alkaline Earth Metals

--quite reactive, also found in comp’d form

--tend to lose 2 electrons (form +2 ions)

(takes more energy to lose 2 electrons!)

6A = Chalcogens

--tend to gain 2 electrons (form -2 ions)

--nonmetals

--oxygen & sulfur – exist in “pure form”

--others – are ions within metal ores

7A = Halogens

--most reactive of nonmetals

--react w/metals to form salts (halides)

--gain 1 electron (form -1 ions)

Types of Representative Elements

8A = Noble Gases--mostly unreactive (inert)--outer energy level is filled, so overall

charge is zero--helium also has a filled outer level, so it is

placed in the noble gas columnHydrogen--most common in universe; very reactive--has 1 p+ and 1 e-

--will lose 1 e- and form +1 ion

Types of Representative Elements

Transition Elements• B elements (metals)

• Arrangement of electrons in outer energy levels vary, so common ion charge changes

• Lose different numbers of valence electrons depending on the reaction

• Degree of reactivity…and therefore properties…varies by element

• Common Ion Charge = +2

Lanthanides & Actinides

• Bottom of P.Table

• Lanthanides (follow Lanthanum)

– Properties of Metals

– Similar to 2A elements

• Actinides (follow Actinium)

– radioactive

Trend #1 – Ionization Energy• Energy needed to remove an electron from an

atom• General Trend = increases to the right and up

– Electron Shielding – outermost e- are held less tightly to nucleus, so easier to lose them (in elements to left)

http://www.shodor.org/chemviz/ionization/students/background.html

Trend #2 - Electronegativity• How strongly an atom attracts electrons (to

itself) in a bond, particularly when e- are shared, which is called covalent bonding.

• General Trend = increases to the right and up

http://grandinetti.org/Teaching/Chem121/Lectures/Electronegativity/assets/ElectronegativityTrends.gif

Trend #3 – Atomic Radius• Essentially – size of atom• Determined by calculating bond radius• Size depends on volume occupied by electrons,

which can change with state of matter and movement of e-

• General Trend = increases to left and down

http://www.shodor.org/chemviz/ionization/students/background.html

Trend #4 – Ionic Radii

• Cations (+ charge)– Generally smaller than parent atom because

of electron loss– Example: Ca | Ca2+

• Anions (- charge)– Generally bigger than parent atom because of

electron gain– Example: P | P3-

• General Trend = increases to left and down

Trend #5 – Electron Affinity

• The energy change that occurs when a neutral atom gains an electron

• Different from electronegativity, which measures an atom’s attraction for e- when bonded to another atom

• General Trend = increases to the right and up

http://www.mcatpearls.com/master/node180.html

The Trends in Summary

http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH08/FG08_17.JPG

From Where Did the Elements Come?

• ~93 in nature (Np, Pm, Tc – in stars)

• Nuclear reactions in stars; Ex: H, He

• Transmutation – a nuclear reaction, where one element changes into another

• Synthetic (lab created) – by transmutation, using particle accelerators; includes all transuranium elements (from #92 on)