5-1 Organizing the Elements
• What does the word “periodic” mean?
• Periodic: recurring at regular intervals
• Periodic table – is an arrangement of elements in columns based on a set of properties that repeat from row to row
Mendeleev 1869• See Figure 3 on page 127• Arranged elements according to
increasing atomic mass in rows• Put elements of similar properties in the
same column• Left blank spots in table which predicted
properties of elements not yet discovered
Evidence Supporting Mendeleev’s Table
• Named eka-aluminum to the element that belonged one space below aluminum on the table
• 1875- French chemist discovered a new element and named it gallium (Ga)
• Gallium is a soft metal used in traffic signals
Similarity of the two• Eka-aluminum and Gallium were
similar in properties, so they were determined to be the same
• The close match between Mendeleev’s prediction and the actual properties of new elements showed how useful his periodic table could be
Questions3. What happens to the composition
of matter during a physical change? Does it change or remain the same?
5-2 The Modern Periodic Table
• Mendeleev developed the periodic table before the discovery of protons.
• In the modern periodic table, elements are arranged by increasing atomic number
Periods • Each row in the table of elements is called a
period• Period 1 has two elements • Periods 2 and 3 have 8 elements• Periods 4 and 5 have 18 elements• Period 6 has 32 elements• There are 7 periods total on the periodic table• The number of electrons per period varies
because of the number of available orbitals increases from energy level to energy level
Groups• Each column on the periodic table is called a
group• The elements within a group have similar
properties• Properties of elements repeat in a predicable
way when atomic number are used to arrange elements into groups
• The pattern of repeating properties is the periodic law
• There are 18 groups on the periodic table
Atomic Mass• Atomic mass is a value that
depends on the distribution of an element’s isotopes in nature and the masses of those isotopes
• An atomic mass unit (amu) is defined as one twelfth the mass of carbon-12 atom
Average Atomic Mass
•Weighted average of the atomic masses of the naturally occurring isotopes of an element
What is the aver. atomic mass of the
chlorine?
Isotope Isotope Mass (amu)
% Abundance
Chlorine-35
34.96885 75.771
Chlorine-37
36.96590 24.229
Weighted Averages• Average Atomic Mass = • (isotope mass)(relative abundance[dec]) + (isotope mass)(relative abundance[dec])
• (0.75771)(34.96885amu) + (0.24229)(36.96590amu)
• = 35.453 amu
ISOTOPES • Atoms of the same element that
differ in mass• Have the same # protons but
different # neutrons
Classes of Elements• Elements are classified as metals, nonmetals, and metalloids
• Metal:– Good conductor of heat & electricity– Ductile –able to be drawn into a fine wire– Malleability – can be hammered or rolled into thin sheets
• Nonmetal– Poor conductor of heat & electricity– Brittle
• Metalloids– Some characteristics of metals & nonmetals
Beaker Breaker1. Isotopes have the same # of _______
but different #of __________
2. What is the name of group 1 on the periodic table?
3. How many periods are there on the periodic table?
Transition Metals• Transition metals are elements
that form a bridge between the elements on the left and right sides of the table
The Lanthanides• The 14 elements with atomic
numbers from 58(cerium, Ce) to 71(lutetium, Lr)
• Similar in chemical and physical properties
Variation across a period
• Across a period from left to right, the elements become less metallic and more nonmetallic in their properties
• Most reactive metals are on the left side of the table
• Most reactive nonmetals are on the right in Group 17
5-3 Representative Groups
• Valence electron – is an electron that is in the highest occupied energy level of an atom
• Elements in a group have similar properties because they have the same number of valence electrons
• Valence electrons explain the location of hydrogen, hydrogen has a single electron
Alkali Metals• Elements in Group 1A are called
alkali metals.• Single valence electron and are
extremely reactive• The reactivity of alkali metals
increases from the top of Group 1A to the bottom
The Alkaline Earth Metals
• The elements in Group 2A are called alkaline earth metals
• All alkaline earth metals have two valence electrons
• They are harder than group 1A
• Differences in reactivity among the alkaline earth metals are shown by the ways they react with water
• Calcium, strontium and barium react easily with cold water
• Magnesium will react with hot water. No change appears to occur when beryllium is added to water
The Boron Family• Group 3A contains the metalloid
boron.• Aluminum is the most abundant
metal in the Earth’s crust• Glass that contains boron is used
to make laboratory glassware such as flasks
The Carbon Family• Group 4A contains nonmetal carbon• Two metalloids – silicon and germanium• Two metals – lead and tin• Except for water, most of the
compounds in your body contains carbon• Silicon is the second most abundant
element in the Earth’s crust
The Nitrogen Family• Group 5A contains two nonmetals
– nitrogen and phosphorus• Two metalloids – arsenic and
antimony• One metal –bismuth• Besides nitrogen, fertilizers often
contain phosphorus
The Oxygen Family• Group 6A has three nonmetals –
oxygen, sulfur, and selenium• Two metalloids – tellurium and
polonium• All have 6 valence electrons• Oxygen is the most abundant
element in the Earth’s crust
The Halogens• The elements in Group 7A are called
halogens• They have seven valence electrons• Despite their physical differences, the
halogens have similar chemical properties
• They are highly reactive nonmetals• Fluorine is the most reactive