Chemistry Helpers
Periodic Table Definitions and Electron Configurations Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Hassium Bohrium Meitnerium Darmstadtium Roentgenium Copernicium Ununtrium Ununquadium Ununpentium Ununhexium Ununseptium Ununoctium Electron Configuration
Periodic Table

Periodic Table Hydrogen Helium Lithium beryllium boron carbon nitrogen oxygen fluorine neon sodium magnesium aluminium silicon phosphorus sulfur chlorine argon potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton hydrogen rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon caesium barium lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon francium radium actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium rutherfordium dubnium seaborgium bohrium hassium meitnerium

 

Classifying Elements
There have been many attempts to classify the elements by their properties:
 A.   Dobereiner's Triads
Cl, Br, I       Ca, Sr, Ba Li, Na, K
 
B.   Newland's Octaves
Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ca
( #8 is similar to #1)       ( #9 is similar to #2)
 
C.   Dmitri Mendeleev's Period Law 1869
Periodic Law:
·        Placed elements in horizontal rows by atomic mass and in columns by chemical properties.
·        Problem: atomic mass doesn’t increase regularly
 
D. Modern Periodic Law:
·        The properties of elements repeat periodically when the elements are arranged in increasing orders by their atomic number.
 
The Modern Period Table:
 
A.   Groups or chemical families
·        these are the vertical columns of the periodic table
·        group # is indicated at the top of the group
·        the main group elements have the same number of valence electrons
·        all elements of a chemical family have the same fundamental chemical properties
·        differences between the elements within a group differ primarily due to their size differences
 
B.   Periods
·        these are the horizontal rows of the periodic table
·        the period # is indicated at the left of the row
·        the period # also indicated the principle energy level
          (the level where valence electrons are being filled)
·        differences between elements in a period are primarily due to differences in nuclear charge
 
C. Metals, Metalloids and Nonmetals
1)    The left 2/3 of the period table (left of the staircase) are METALS.
·        As you proceed left in a period, or down in a group, the metallic properties of an element will INCREASE.
·        The most metallic element on the periodic table is Fr--FRANCIUM.
a)    Properties of metals:
1.       shiny or lustrous
2.       malleable (can be hammered into shapes)
3.       ductile (can be stretched) i.e. can be stretched into wires
4.          good conductor of electricity
5.          high melting and high boiling points
 
2)    The right 1/3 of the periodic table (right of the staircase) are NONMETALS.
·        As you proceed right in a period or up in a group, the nonmetallic properties of an element will INCREASE.
·        The most nonmetallic element on the periodic table is F—FLUORINE
a)    Properties of nonmetals
1.          hard
2.          brittle
3.          poor conductors of electricity
4.          low melting and low boiling points
 
3)    The elements on the staircase are called METALLOIDS
·        These have properties of both metals and nonmetals
·        They include B, Si, As, Te, At, Ge, Sb, Po.
(Boron, Silicon, Arsenic, Tellurium, Astatine, Germanium, Antimony and Polonium)
**exception: Aluminum which is a metal**
 
Determining Solid, Liquid or Gas
*If the melting and boiling points are both below 273K it will be a gas.
*If the melting point is below 273K but the boiling point is above 273K it will be a liquid.
*If the melting and boiling points are both above 273K it will be a solid
 
Questions
1.                Which elements on the periodic table exist as diatomics at STP?
Br2 I2 N2 Cl2 H2 O2 F2
            (bromine, iodine, nitrogen, chlorine, hydrogen, oxygen, fluorine)
 
2.                Which elements on the periodic table exist as monatomics at STP?
The noble gases, group 18
He, Ne, Ar, Kr, Xe, Rn
(helium, neon, argon, krypton, xenon and radon)
 
3.                Which elements on the periodic table exist as gases at STP?
The noble gases (group 18), H, N, O, F
He, Ne, Ar, Kr, Xe, Rn
(helium, neon, argon, krypton, xenon, radon, hydrogen, nitrogen, oxygen and fluorine)
 
4.                Which elements on the periodic table exist as liquids at STP?
Br, Hg
(bromine, mercury)
 
5.                Which group(s) contain elements that are solid, liquids or gases?
Group 17
Gases: fluorine, chlorine
Liquid: bromine
Solids: iodine and astatine
 
 
Electron Configurations:
          Every group has a corresponding electron configuration and name:
 
                   Group 1    The Alkali metals
·   each element has one valence electron in its outermost orbital
·        Very reactive, not found in nature as elements
·        All lose 1 electron to form a +1 ion (cation)
 
                   Group 2    The Alkaline Earth metals
·        each has two valence electrons in its outermost orbital
·        less reactive than group 1, but still not found free in nature as elements
·        all lose 2 electrons to form a +2 ion (cation)
 
                   Group 17 The Halogens
·        each has seven valence electrons
·        each gain 1 electron to form a -1 ion (anion)
         
                     Group 18 The Noble Gases
                   ·        All noble gases have the stable octet noble gas configuration ( 8 valence electrons) , except He, and therefore do not gain or lose electrons.
 
                     Groups 3-12   Transition Metals
· form colored ions in solutions
·     used in tools, wire, jewelry and coins
 
                      Inner transition metal
· the lanthanoid and actinoid series
 
*All other groups will be named for the first element in that group.
 
A.   ATOMS VS. IONS
**Goal: all elements are seeking a noble gas configuration**
 
1) Metals are atoms that LOSE electrons to form a POSITIVE ion.
·        POSITIVE ions are SMALLER than their neutral atoms.
 
2) Nonmetals are atoms that GAIN electrons to form a NEGATIVE ion.
·        NEGATIVE ions are LARGER than their neutral atoms.
 
 
Periodic Trends
A.      Factors that determine periodic trends:
1.                Nuclear charge- affects trends in a period
·        Increased # protons, increased attraction for electrons
2.                Atomic size - affects trends in a group
·        The further away the electrons are from the nucleus, the less they are attracted to it.
3.                Shielding - affects trends in a group
·        The core electrons shield the valence electrons from the positive charge of the nucleus.
 
B.      Covalent Atomic Radius (Table S)
·   half the distance between two nuclei in a solid crystal  
·     Trend from left to right (within a period) = DECREASES
·     Trend from top to bottom (within a group) = INCREASES
 
C.   Ionic Radius: (no table, estimate using Table S)
·         An atom that has gained or lost electrons will change in atomic size
·         Metals tend to lose electrons so the ionic radius will be smaller than the covalent atomic radius.
·        Nonmetals tend to gain electrons so the ionic radius will be larger than the covalent atomic radius.
D.   Ionization Energy (Table S)
· the amount of energy required to remove the most loosely held valence electrons from a neutral atom in the gaseous state.
·     Trend from left to right (within a period) = INCREASES
·     Trend from top to bottom (within a group) = DECREASES
 
E.   Electronegativity (Table S)
· the measure of attraction an atom has for a pair of electrons
· Trend from left to right (within a period) = INCREASES
· Trend from top to bottom (within a group) = DECREASES
 
F.    Reactivity:  the transfer (gain or lose) of electrons
·        Metals are more active toward the bottom left corner where electrons are mostly easily lost.
·        Nonmetals are more active toward the upper right corner where electrons are most easily gained.
·        Noble gases have no (or minimal) reactivity and this is why they weren't discovered for many years.
 
Summary:
·        Within a period, as the atomic number increases:
                   1. covalent atomic radius               DECREASES
                   2. ionization energy                        INCREASES
                   3. electronegativity                         INCREASES
                   4. metallic character                      DECREASES
 
·        Within a group, as the atomic number increases:
                   1. covalent atomic radius               INCREASES
                   2. ionization energy                        DECREASES
                   3. electronegativity                         DECREASES
                   4. metallic character                      INCREASES
 
 
PERIODIC TRENDS
1. The lowest ionization energy in any period is the element from group 1.
2. The highest ionization energy in any period is the element from group 18.
3. The highest covalent radius in any period is the element from group 1.
4. The lowest covalent radius in any period is the element from group 17.
5. The lowest electronegativity in any period is the element from group 1.
6. The highest electronegativity in any period is the element from group 17.
7. The lowest ionization energy in any group is the element from period 7.
8. The highest ionization energy in any group is the element from period 1.
9. The highest covalent radius in any group is the element from period 7.
10. The lowest covalent radius in any group is the element from period 1.
11. The lowest electronegativity in any group is the element from period 7.
12. The highest electronegativity in any group is the element from period 1.
13. The element with the highest ionization energy in the period table is He.
14. The element with the lowest ionization energy in the period table is Fr.
15. The most reactive metal on the periodic table is Fr.
16. The most reactive nonmetal on the periodic table is F.
17. The group with the most valence electrons is group 18.
18. The group with the fewest valence electrons is group 1.
19. The element with the largest nuclear charge in any period is from group 18.
20. The element with the largest nuclear charge in any group is from period 7.

 

 

 

Here is the answer to balancing equations:  It seems that this unit is being taught early in your high school, but let's go through the general procedures for balancing equations.
*We must always remember the Law of Conservation of Mass - it cannot be created or destroyed, only transferred.  What that means is that what you have on one side of the reaction must be equal on the other side of the reaction as well.  If I have 2 carbons on the reactant side, I must also have 2 carbons on the product side.
*Use the subscripts & coefficients to count each element (some students find it easier to create a chart- simply put the elements present in the middle and then count the number of each and write them on the corresponding side).
 

Ex:          _______H2 +   _______ O2  →   _________ H2O
 
 
                                                               2          H         2
                                                               2          O         1
 
We need to balance (you cannot change the subscripts and you cannot remove anything) – hydrogen is good because we have 2 on each side, however oxygen is not balanced. If we add the coefficient 2 on the product side to balance the oxygen, we have also changed the hydrogen.
 
2          H         2   4
                                                                2          O         1   2
 
_______H2 +   _______ O2  →   2 H2O
 
Now we need to balance the hydrogen by placing the coefficient 2 on the reactant side.
 
2H2 +   _______ O2  →   2H2O
 
Let’s look at the chart again:
                                                                  4 2          H         2   4
                                                                     2          O         1   2
 
You now have a balanced equation.


Write Your Questions Below



how to balance equations
October 7, 2011

Please see above.

October 7, 2011 -  Replied By Expert

If the mass number is the total number of protons and neutrons, how can the mass be a decimal? Can there be a portion of a neutron?
September 24, 2011
There are no partial protons, neutrons or electrons. The reason for the decimal is because of isotopes which is when an element has different numbers of neutrons which then cause different masses. These masses are then averaged.
September 24, 2011 -  Replied By Expert

 
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