Elemental Properties and Patterns Periodic Trends Elemental Properties and Patterns

The Periodic Law Dimitri Mendeleev was the first scientist to publish an organized periodic table of the known elements.

The Periodic Law Mendeleev even went out on a limb and predicted the properties of 2 undiscovered elements. He was very accurate in his predictions, which led the world to accept his ideas about periodicity and a logical periodic table.

Mendeleev’s Prediction

Mendeleev arranged the elements by increasing atomic mass. The modern periodic table is in order of increasing atomic number. Mosley is given credit for arranging by atomic number.

The Periodic Law When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.

The Periodic Law Atoms with similar properties appear in groups or families (vertical columns) on the periodic table. They are similar because they all have the same number of valence (outer shell) electrons, which governs their chemical behavior.

Valence Electrons Do you remember how to tell the number of valence electrons for elements in the s- and p-blocks? How many valence electrons will the atoms in the d-block (transition metals) and the f-block (inner transition metals) have? Most have 2 valence e-, some only have 1.

A Different Type of Grouping Besides the 4 blocks of the table, there is another way of classifying element: Metals Nonmetals Metalloids or Semi-metals.

Metals, Nonmetals, Metalloids

Metals, Nonmetals, Metalloids There is a zig-zag or staircase line that divides the table. Metals are on the left of the line, in blue. Nonmetals are on the right of the line, in orange.

Metals, Nonmetals, Metalloids Elements that border the stair case, shown in purple are the metalloids or semi-metals. There is one important exception. Aluminum is more metallic than not.

Metals Metals are lustrous (shiny), malleable, ductile, and are good conductors of heat and electricity. They are mostly solids at room temp. What is one exception?

Nonmetals Nonmetals are the opposite. They are dull, brittle, nonconductors (insulators). Some are solid, but many are gases, and Bromine is a liquid.

Metalloids They have characteristics of both metals and nonmetals. They are shiny but brittle. And they are semiconductors. What is our most important semiconductor?

Periodic Trends - Important Concepts Valence electrons- electrons in the outermost energy level Core electrons- electrons in the inner energy levels When an atom loses an electron, which electron is removed? valence

Effective Nuclear Charge (Zeff) What keeps electrons from simply flying off into space? Effective nuclear charge is the pull that an electron “feels” from the nucleus. The closer an electron is to the nucleus, the more pull it feels. (Higher Zeff) As effective nuclear charge increases, the electron cloud is pulled in tighter.

Shielding Effect The core electrons in an atom “shield” the valence electrons from the pull of the nucleus As the shielding increases (more e- between nucleus and valence e-), the effective nuclear charge _________. decreases

Bohr Models

Sodium and Potassium

Applications Which atom (Na or K) is a larger atom? Why? Which atom has more shielding? Which atom has a higher effective nuclear charge? Which atom would require less energy to remove the valence electron? (easiest to remove)

Atomic Radius (Size) The trend for atomic radius in a vertical column is to go from smaller at the top to larger at the bottom of the family. Increases down the group. Why? With each step down the family, we add an entirely new energy level to the electron cloud, making the atoms larger.

Atomic Radius The trend across a horizontal period is less obvious. What happens to atomic structure as we move from left to right across a period? Each step adds a proton and an electron (and 1 or 2 neutrons). Electrons are added to existing energy levels or sublevels, we don’t add a new energy level.

Atomic Radius The effect is that the more positive nucleus has a greater pull on the electron cloud. The nucleus is more positive and the electron cloud is more negative. The increased attraction pulls the cloud in, making atoms smaller as we move from left to right across a period. The Zeff increases but the shielding does not change.

Atomic Radius decreases increases

Practice 1. Arrange the following in order of increasing size: O, Se, S O, S, Se P, Mg, Cl Cl, P, Mg S, F, Rb F, S, Rb P, Ga, O O, P, Ga

Ionization Energy If an electron is given enough energy (in the form of a photon) to overcome the effective nuclear charge holding the electron in the cloud, it can leave the atom completely. The atom has been “ionized” or charged. The number of protons and electrons is no longer equal.

Ionization Energy The energy required to remove an electron from an atom is ionization energy. (measured in kilojoules, kJ) The larger the atom is, the easier its electrons are to remove. Ionization energy and atomic radius are inversely proportional. Ionization energy is always endothermic, which means energy is added to the atom to remove the electron.

Ionization Energy As you move down a group, the ionization energy decreases. It becomes easier to remove the valence electron. Why? As you move across a period, the ionization energy increases.

Ionization Energy increases decreases

Exceptions (Honors) *does not vary uniformly across period*   2nd period in order of increasing I.E.  Li, B, Be, C, O, N, F, Ne     Why?

Practice 1. Arrange in order of increasing ionization energy: Br, Cl, I I, Br, Cl Sb, Sr, I Sr, Sb, I C) (Honors) Ge, As, Se Ge, Se, As

Electron Affinity (Honors) What does the word ‘affinity’ mean? Electron affinity is the energy change that occurs when an atom gains an electron (also measured in kJ). Where ionization energy is always endothermic, electron affinity is usually exothermic, but not always.

Electron Affinity (Honors) Electron affinity is exothermic if there is an empty or partially empty orbital for an electron to occupy. If there are no empty spaces, a new orbital or energy level must be created, making the process endothermic. This is true for the alkaline earth metals and the noble gases.

Metallic Character (Activity of Metals) Which family of metals would be the most reactive? Why? As you move down a group, the activity of metals increases. As you move across a period, the activity of metals decreases.

Activity of Metals The activity of metals is based on how easily the metal loses an electron. Very active metals lose their valence electrons easily.

Activity of Metals decreases increases

Examples 1. What is the most active metal Ca, Be, Sr Sr Sc, K, Ca K Pd, Cd, Sr

Nonmetallic Character (Activity of Nonmetals) What family is the most active of the nonmetals? Why? As you move down a group, the activity of nonmetals decreases. As you move from left to right across a period, the activity of nonmetals increases. What is the most active nonmetal? F

Activity of Nonmetals The activity of nonmetals is based on how easily an atom will gain an electron. Very active nonmetals have a strong attraction for electrons.

Activity of Nonmetals increases decreases Do not include the noble gases!

Way To Remember The Trends What trends increase down a group and across a period? decrease increase size, activity of metals

What is the Name of the Snowman? Size Activity of Metals

Ionic Radius Cations are always smaller than the original atom. The valence electrons are removed during ionization. Ca2+ is ____________than Ca. Conversely, anions are always larger than the original atom. Electrons are added to the outer energy level. S2- is _____________than S.

Cation Formation Effective nuclear charge on remaining electrons increases. Na atom 1 valence electron Remaining e- are pulled in closer to the nucleus. Ionic size decreases. 11p+ Valence e- lost in ion formation Result: a smaller sodium cation, Na+

Anion Formation A chloride ion is produced. It is larger than the original atom. Chlorine atom with 7 valence e- 17p+ One e- is added to the outer shell. Effective nuclear charge is reduced and the e- cloud expands.

Examples 1. Arrange from smallest to largest: A) H, H+, H- H+, H, H- B) K+, Cl-, S-2, Ca+2 Ca+2, K+, Cl-, S-2 2. Given the following elements, which would be the largest when forming an ion? Br, Se, Rb, Sr Se 2-