# Chapter 5 Organizing The Elements

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Chapter 5 Organizing The Elements

OBJECTIVES Describe how Mendeleev arranged the elements in his table
Explain how the predictions Mendeleev made and the discovery of new elements demonstrated the usefulness of his periodic table Describe the arrangement of elements in the modern periodic table Explain how the atomic mass of an element is determined and how atomic mass units are defined

Identify general properties of metals, nonmetals, and metalloids
Describe how properties of elements change across a period in the periodic table Relate the number of valence electrons to groups in the periodic table and to properties of elements in those groups Predict the reactivity of some elements based on their locations within a group Identify some properties of common A group elements

In 1750 scientists had identified only 17 elements most of these were metals
As the number of identified elements grew so did the need for organization In 1789 Antoine Lavoisier grouped elements according to categories called metals, non-metals, gases and earths

In 1860 Mendeleev (Russian) needed to describe the now known 63 elements to his students
On cards, he listed the name, mass and properties of the 63 elements He arranged them in order of increasing atomic mass. He was able to break the elements into rows (see pg 127 Fig. 3 and columns based on the properties of the elements

Columns increased from TOP to BOTTOM
He knew that not all elements were discovered yet so he left room for them Properties of elements are related to its location in the table Review questions 1-5 pg. 129

5.2 Modern Periodic law In the modern periodic table, elements are arranged by increasing ATOMIC NUMBER (number of protons) PERIODS Each row in the periodic table is a period Ex. Period 1 has 2 elements period 2 and 3 have 8 elements The number of elements in each period varies because of the available orbitals increase from energy level to energy level

In other words the first energy level has only 1 orbital so, the 1 electron in a H atom and the 2 electrons in a He atom can fit in this orbital But Li contains 3 electrons so 2 can fit in the 1st orbital and the other electron has to go in the 2nd orbital(or energy level) this is why Li is the first element in Period 2

Na (sodium) the first element in period 3 has one electron in its 3rd orbital or energy level
K (potassium), the first element in Period 4 has one electron in its 4th orbital This pattern applies to all elements in the first column on the table

GROUPS (FAMILIES) Each COLUMN is called a group or family The elements within a group have similar properties (electron configurations) The electron configuration determines the chemical properties THE PATTERN OF REPEATING CHEMICAL PROPERTIES IS CALLED PERIODIC LAW REFER TO FIG. 7 PGS

Atomic Mass Copy Fig. 8 into your notebook There are 4 pieces of information for each element Name of the element, its symbol, its atomic number, and its atomic mass(the number of isotopes and their mass in nature) Atoms of 2 isotopes have different atomic masses(isotopes have different # of neutrons than protons) they are usually equal

Classes of Elements Solids, liquids, gases based on their state at room temperature Symbols solids (black) liquid (purple) gas (red) Elements are divided into those that occur naturally and those that do not Ex. Elements with an atomic number of 93 or above DO NOT OCCUR NATURALLY 1-92 occur naturally

Third classification is based on general properties
Metals—located on left (blue) Non-metals located on right (yellow) Metalloids located in the middle (green)

METALS Majority of elements are metals Represented by blue boxes Good conductors of heat Electric current Solid at room temperature (except mercury) Most are malleable Many are ductile (able to be drawn into thin wire)

Groups 3 through 12 are referred to as transition metals
These transition metals form a bridge between the elements on the left and right One property of these metals is their ability to form compounds with distinct colors Ex. Tinted glass They are among the 1st elements discovered

NONMETALS Represented by yellow boxes Have properties opposite to those of metals Poor conductivity of heat and electric Low boiling points Many are gases at room temperature Are brittle (will shatter or crumble)

METALLOIDS Represented by green boxes Properties of these elements fall somewhere between metals and nonmetals Their ability to conduct heat or electric depends on their temperature

Variation across a Period
Changes in the properties of elements change in a similar way when you move from left to right (except for period 1) From left to right, elements become less metallic and more nonmetallic Most reactant elements or on the left side of the table Most reactive nonmetals are on the right side (group 17) Copy fig. 13 into your notebooks Complete questions 1-5 and 7

Valence electrons An electron that is in the highest occupied energy level of an atom Valence electrons play a key role in chemical reactions The properties of elements vary because the number of valence electrons increases from left to right

Remember that elements in a group have similar properties because they have the same number of valence electrons Ex. Hydrogen and Lithium have I valence electron

Alkali metals elements in group 1A
1 valence electron Highly reactive Ex. Sodium chloride (table salt) Group 1A Li, Na, K, Rb, Cs, Fr Their reactivity increases from TOP TO BOTTOM

Alkaline Earth metals Group 2A Contain 2 valence electrons Harder than metals in group 1A Differences in reactions with water Calcium and magnesium are essential to biological functions

Magnesium Key role in photosynthesis Mixture of magnesium and other metals can be as strong as steel but much lighter Calcium Keeps bones and teeth strong, toothpastes may contain calcium to polish teeth Plaster casts contain calcium sulfate

The Boron Family Group 3A Contain 3 valence electrons Aluminum(metal) most abundant metal in the earth’s crust Boron(metalloid)

The Carbon Family Group 4A 4 valence electrons Contains 1 nonmetal(carbon) 2 metalloids(silicon, germanium) 2 metals(tin, lead) Life on earth would not exist without carbon, most compounds in your body contain carbon Silicon is the 2nd most abundant element in the crust

The Nitrogen family Group 5A Contain 5 valence electrons Contain 2 nonmetals(arsenic, antimony) 1 metal(bismuth) 1 nonmetal gas (nitrogen) 1 solid nonmetal(phosphorus) In this group phosphorus and nitrogen are most important Contained in fertilizers and compounds in your body to release energy

The Oxygen family Group 6A Contain 6 valence electrons 3 nonmetals (oxygen, sulfur, selenium) 2 metalloids (tellurium, polonium) Oxygen is the most abundant element in the earth’s crust Can be stored as a liquid, under pressure Ozone is another form of oxygen ground level is an eye irritant, in the atmosphere absorbs radiation

The Halogens Group 7A 7 valence electrons Highly reactive nonmetals 2 gases (fluorine, chlorine) 1 liquid (bromine) 1 solid (iodine) All react easily with most metals

Fluorine compound used to prevent tooth decay, non-stick coatings
Chlorine is in bleach, and used to kill bacteria in drinking water and pools (bromine for hot tubs) Your body needs iodine to keep your thyroid gland working properly

The Noble Gases Group 8A 8 valence electrons (except helium) (2) This means these elements have a full outer shell This group does not react with any other elements Questions 1-10 page 145 Internet activity—see if you can find the 25 essential elements to the human body and 3 elements that should be avoided completely