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)
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