Periodic Trends

Which of the following have the largest atomic radii within their respective periods? (Transition metals, Noble gases, Alkali metals, Halogens)

Alkali metals ; The alkali metals are found in the first group (column) of the periodic table, on the leftmost side. They have only 1 loosely bound electron in their outermost shells, and their effective nuclear charge values are low, giving them the largest atomic radii of all the elements in their periods.

Below are the data for ionization energies of three elements X, Y and Z. These elements are on the third period of the periodic table. The first four ionization energies for elements X, Y and Z are given below: X: IE1 - 498.9 IE2 - 4562 IE3 - 6910.3 IE4 - 9543 Y: IE1 - 577.5 IE2 - 1816.7 IE3 - 2744.8 IE4 - 11577 Z: IE1 - 737.7 IE2 - 1450.7 IE3 - 7732.7 IE4 - 10542.5 (Ionization energies in kJ/mol for elected elements. What type of element is element Z? (Halogen, Alkali metal, Noble gas, Alkaline-earth metal)

Alkaline-earth metal ; We see that element Z is magnesium due to its ionization energy discrepancy between IE2 and IE3. It is in the second group, therefore making it an alkali earth metal. Remember that elements in the same group exhibit similar chemical properties.

Which of the following has the smallest atomic radius? (Rb, K, Na, Cs, Li)

Li ; Atomic radius INCREASES DOWN and TO THE LEFT in the periodic table

ionization energy

The amount of energy required to remove an electron from an atom

atomic radius trend

decreases from left to right increases from top to bottom

electronegativity trend

decreases from top to bottom in a group; increases from left to right in a period

ionization energy trend

decreases from top to bottom in a group; increases from left to right in a period

electron affinity trend

increases up and to the right

atomic radius

one-half the distance between the nuclei of two atoms of the same element when the atoms are joined

Periodic Trends

property of the elements that can be predicted from the arrangement of the periodic table

electronegativity

the ability of an atom to attract electrons when the atom is in a compound

electron affinity

the energy change that occurs when an electron is acquired by a neutral atom

Which of the following has the highest electronegativity? (Mg, S, Cl, Ba)

Cl ; It is the furthest to the right and up. Electronegativity measures the ability an atom to attract shared electrons in bond. It follows a trend that it increases moving from left to right and down to up across the periodic table.

Which of the following elements has the largest atomic radius? (Cs, Na, Sr, I, F)

Cs ; Atomic radius increases down the columns and to the left. The furthest left elements are Na and Cs. Cs is furthest down so it is the biggest.

Which of the following elements is the least electronegative? (Fe, Cs, F, S, N)

Cs ; Electronegativity increases as one moves left to right across the periodic table, it also increases as one moves up the periodic table. This is because of the changes in the atomic radii of elements that occurs as one move in these directions. Flourine is the most electronegative element because the positive charge of its nucleus exerts the strongest attractive force on it's electrons when compared to the other elements. Conversely, the nuclei of the elements in the lower left hand side of the periodic table exert the weakest attractive force on their electrons when compared to the other elements. As one moves from left to right within the same period, one electron and one proton are added to each element. The electrons will not be any further away from the than the previous element but there will be one more proton with which to generate attractive force on the electrons. So the upper left hand elements have the most protons within their respective period with which to generate pull on the electrons. The electrons of these species are also the closest in proximity to the nucleii.

When considering trends in the periodic table of elements, how do the atomic radii of elements IN THE SAME PERIOD change as one moves from left to right?

Decreasing ; If we look at elements of the same period the principal quantum number for each one of these elements is the same. Thus the outermost energy level for the electrons of each atom is the same. If we consider moving through the periodic table in numerical order, the left side of the periodic table features atoms that have just begun to add electrons to new energy levels. On the right side of the periodic table the elements are moving closer to filling the energy level. The differences in atomic radii are the result of differing amounts of protons between atoms whose electrons are in the same energy level. K has one electron in the fourth energy level and Kr has eight electrons in the fourth energy level. K has 19 protons with which to generate pull on the electrons. Kr has 36 protons with which to generate pull on the electrons. Thus, Kr has a smaller atomic radius because of its ability to have a tighter grasp on its electrons because of the stronger charge generated by its nucleus.

ionic radius

Distance from the center of an ion's nucleus to its outermost electron

Which of the following has the greatest ionization energy? (Ca, Br, Li, F, Na)

F ; Ionization energy goes up across the period and down as you go down the group. This is the energy required to remove an electron. Of the listed elements it would be hardest to remove an electron from Flourine as the positive nucleus close to the electron orbitals has greater attractive force.

Why does fluorine have a smaller atomic radius than carbon?

Fluorine has more charged particles attracting the electron cloud to the nucleus Atomic radius decreases as you move left to right on the periodic table. As atomic number increases, so does the number of positive protons in the nucleus. To the far left of a period, electrons are widespread within a new electronic shell. To the far right of the period, the electrons still occupy the same shell, but experience greater attractive force toward the nucleus due to the higher number of protons present. While it is true that flourine is the most electronegative element, this does not influence atomic radius (though the two trends follow similar patterns).

Which of the following has the LARGEST atomic radius? (H, Rn, Fr, F, Na)

Fr ; Atomic radius expands down the columns and to the LEFT.

Place the following atoms in order of increasing atomic radii: Na, Mg, K, Ca, Rb

Mg, Na, Ca, K, Rb ; The periodic table allows you to follow general guidelines or "trends" that are displayed on the table. Atomic radius is one such trend. As you move down in groups, further shells are added to the atom which results in an increase in radius. As you move to the right on the periodic table, the nuclear charge increases which pulls the electrons closer to the nucleus. As a result, the atomic radius will decrease when moving to the right.