Copper, silver, and gold
Name a few elements that have been known for thousands of years.
13
How many elements had been identified by the year 1700?
Yes
Did chemists suspect that other elements existed?
They were unable to isolate the elements from their compounds
Why couldn’t chemists classify unknown elements even though they had already assigned names to them?
Chemists began to use scientific methods to search for elements
Why did the rate of the discovery of elements increase after 1700?
5
How many elements did chemists discover in 1765-1775?
Hydrogen, nitrogen, and oxygen
What were the three colorless gases that chemists discovered in 1765-1775?
A logical way to organize the elements
What did chemists need to do in order to find out if there was a limit to the number of elements and when they have discovered all of them?
The properties of elements
What did chemists use to sort elements into groups?
Published a classification system for the elements
J.W. Dobereiner
Elements were grouped into triads
Describe the J.W. Dobereiner classification system for the elements.
A set of three elements with similar properties
Triad
One element in each triad tended to have properties that fell midway between those of the other two elements
What was Dobereiner’s pattern in his triads?
Published a table of elements in 1869; inspired Lothar Meyer
Dmitri Mendeleev
Medeleev published his table first and was better fit to explain its usefulness
Why was Mendeleev given more credit than Meyer?
Groups based on a set of repeating properties
How are elements in the periodic table arranged?
In order of increasing atomic mass
How did Mendeleev arrange the elements in his periodic table?
So that the undiscovered elements with similar properties could be put in the same group
Why did Mendeleev leave spaces in his periodic table?
The close match between the predicted and actual properties of gallium helped gain wider acceptance for Mendeleev’s periodic table
What effect did the discovery of gallium have on the acceptance of Mendeleev’s table?
Using atomic mass to organize the periodic table because Medeleev developed his table before the discovery of the structure of atoms
What was the problem that occurred with the pairs of elements on Mendeleev’s periodic table?
Physical and chemical properties
What do the elements in the columns of the periodic table have alike?
A British physicist who determined an atomic number for each known element
Henry Moseley
When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties
Periodic Law
It determines its location (group) in the periodic table (outer electrons have similar sub-level structure because they react chemically the same)
Why should there be a connection between an element’s electron configuration and its location on the periodic table?
An organization that sets standards for chemistry that proposed a new system for labeling groups on the periodic table that we use now
The International Union of Pure and Applied Chemistry
Metals, nonmetals, and metalloids
The three classes of elements
A periodic representation of their physical and chemical properties
What pattern is revealed when the elements are arranged in a periodic table in order of increasing atomic number?
Less, more
Across a period, the properties of elements become _______ metallic and _______ nonmetallic.
– Sheen
– Good conductors of electricity and heat
– Solid at room temperature (except for mercury)
– Malleable
– Ductile (make metals into the form of a wire)
– Good conductors of electricity and heat
– Solid at room temperature (except for mercury)
– Malleable
– Ductile (make metals into the form of a wire)
Metals
Nonmetals
Would you expect metals or nonmetals in the same period to have higher ionization energies?
The trend is for ionization energy to increase from left to right across a period
Why do nonmetals have higher ionization energies in the same period?
– Not shiny
– Poor conductors of electricity and heat (except carbon)
– Gases at room temperature (except sulfur, phosphorus, and bromine)
– Not malleable
– Poor conductors of electricity and heat (except carbon)
– Gases at room temperature (except sulfur, phosphorus, and bromine)
– Not malleable
Nonmetals
Metalloids have properties that are similar to those of metals and nonmetals depending on the conditions
In general, how are metalloids different from metals and nonmetals?
– May behave like a metal or nonmetal
– Can be controlled by changing the conditions
– Can be controlled by changing the conditions
Metalloids
The symbols and names of the elements and information about the structure of their atoms
What does the periodic table display?
Group 1A elements
Alkali Metals
Group 2A elements
Alkaline/Alkali Earth Metals
Group 7A elements
Halogens
Group 8A elements (rarely take part in a reaction)
Noble Gases
Group B elements (the highest occupied s sub-level)
Transition Metals
The rarest elements
Inner Transition Metals (a.k.a. Rare Earth Metals)
They did not fit on the paper
Why are the inner transition metals at the bottom of the Periodic Table instead of the middle?
The distance between the nuclei of atoms (atomic radius)
What can be used to estimate the size of atoms?
The atoms in each molecule are identical
Why can the distance between the nuclei of atoms be used to estimate the size of atoms?
One half of the distance between the nuclei of two atoms of the same element when the atoms are joined
Atomic radius
From top to bottom
How does atomic size increase within a group?
Left to right
How does atomic size decrease across a period?
The nucleus “shields” itself further and further so the electrons explore higher orbitals, calling for a larger atom
Shielding effect of groups
Constant for all the elements in a period; however, the nuclear charge pulls the electron in the highest occupied level energy level closer to the nucleus and the atomic size decreases
Shielding effect of periods
The shielding effect
What is more powerful: nuclear charge, or shielding effect?
Atom(s) that has lost or gained electrons (has a positive or negative charge)
Ion
It has equal number of protons and electrons
Why is an atom electrically neutral?
When electrons are transferred between atoms
How do positive and negative ions form?
By losing one or more electrons from their highest occupied energy levels
How do atoms of metals tend to form ions?
It will get smaller
If an atom loses its outside electrons, how will the size of the atom change?
An ion with a positive charge
Cation
As a number followed by a plus sign (1+)
How is the charge for a cation written?
By gaining one or more electrons
How do atoms of nonmetals form ions?
It will get bigger
If an atom gains an outside electron, how will the size of the atom change?
An ion with a negative charge
Anion
As a number followed by a minus sign (1-)
How is the charge for an anion written?
To higher energy levels
Where do electrons move when atoms absorb energy?
The energy required to move an electron from an atom
Ionization energy
When an element is in its gaseous state
When is ionization energy measured?
first ionization charge
The energy required to move the first electron from an atom is called the ________.
decrease, increase
First ionization energy tends to ________ from top to bottom within a group and ___________ from left to right across a period. (increase, decrease)
Remove an electron from an ion with a 1+ charge (the ion produced has a 2+ charge)
What is the second ionization energy required to do?
Remove an electron from an ion with a 2+ charge (the ion produced has a 3+ charge)
What is the third ionization energy required to do?
It is relatively easy to remove the first electron from an alkali metal atom; it is much more difficult to remove the second because it is in a larger energy level
Why is there a large increase between the first and second ionization energies of alkali metals?
What ions elements will form
What can ionization help you predict?
The ability of an atom of an element to attract electrons when the atom is in a compound
Electronegativity
decrease, increase
In general, electronegativity values _______ from top to bottom within a group and _________ from left to right across a period. (increase, decrease)
