Periodic Trends
Understand that many properties of elements can be predicted by looking at a periodic table. We are going to look at 9of these properties. Atomic Radius Ionization Energy Electron Affinity Electronegativity Density Melting Point Shielding Effect Metal reactivity Non-metal reactivity
Atomic Radius Atomic Radius is defined as one-half the distance between the nuclei of identical atoms that are bonded together. How big am I?
The Trend for Atomic Radius Left to right the size gets smaller As you go across a row, more and more protons are being added to the nucleus Which means the nuclear charge is increasing There is a much stronger pull on the electrons Thus, the electron cloud shrinks Top to bottom the size gets bigger Common sense; as you go down the group, the energy level number increases size increases
Ionization Energy Ionization Energy is the energy required to remove the most loosely held electron from a gaseous atom or ion. How much do I really like my outer electrons?
The Trend for Ionization Energy Left to right the energy increases The more protons in the nucleus, the higher the nuclear charge, the tighter the hold on the electrons There are some peaks and valleys along the way Top to bottom the energy decreases The farther the electrons are from the nucleus, the easier it is to remove them
Electron Affinity Electron Affinity is the energy change that occurs when a neutral atom gains an electron. Do I really want an extra electron?
The Trend for Electron Affinity Left to right it generally increases across the row But, there are some elements that do not want extra electrons Look at the noble gases.must forced them to add an electron Top to bottom it slightly decreases going down a group
Electronegativity Electronegativity is a measure of the tendency of an atom to attract a pair of electrons to itself when in a bond with another atom. Am I nice at sharing electrons?
The Trend for Electronegativity Left to right electronegativity tends to increase as you go across a row Notice that the top three noble gases do not have an electronegativity In the early 1960s, it was determined that highly electronegative fluorine could react with krypton to make a stable compound Top to bottom electronegativity generally decreases as you go down a group
Density Density is determined by dividing the mass of the object by its volume. How compact am I?
The Trend for Melting Point Left to right the trend gradually increases, then decreases (increases through metals, decreases through the non-metals) Top to bottom the trend increases as you go down a group
Melting Point Melting Point is the temperature at which something melts. This is directly tied to the force of attraction between the particles. Do I like my brother?
Trend for Melting Point Left to right the trend fluctuates; increases across until about Group 4 (14), then drops Top to bottom the trend generally decreases down a group
Shielding Effect This is the effect of full energy levels separating the outer energy electrons from the nucleus How many fences are blocking the electrons from the nucleus?
Trend for Shielding Effect Left to right the shielding effect is the same for any row Top to bottom shielding effect increases as you go down a group
Metal Reactivity Left to right the most reactive metals are found in Group 1; the alkali metals Top to bottom in any group of metals, the most reactive metal is at the bottom of the group
Non-metal Reactivity Left to right the most active non-metals are found in Group 7 (17); the halogens Top to bottom in a group of non-metals, the most active non-metal will be at the top of the group
Most active metal Most active non-metal
Summary