Aim: How can we describe the arrangement of the periodic table? Do Now: 1.Take out a calculator and periodic tables. 2.Describe what information can be found on the periodic table of elements.

Information we can find on the periodic table of elements

How is the periodic table arranged? Dmitri Mendeleev is given credit for first arranging the elements in a usable manner. Mendeleev noticed that when elements were arranged in order of increasing atomic mass, similar chemical and physical properties appeared at regular (periodic) intervals. However, there were some irregularities with Mendeleev’s arrangement, so the modern periodic table arranges the elements by their atomic number. Modern periodic law states that the properties of elements are periodic functions of their atomic numbers.

How is the periodic table arranged? The periodic table is arranged in horizontal rows called periods and vertical columns called groups (sometimes families).

Properties of Periods The number at the beginning of the period indicates the energy level in which valence electrons are located for the atoms of that period. Example: Potassium (K) and Bromine (Br) are members of period 4. Which energy level can their valence electrons be found on? The number of valence electrons increases from left to right in a period. Each period of the table ends with a noble gas.

Trends in a Period 1.Ionization Energy – What happens to the first ionization energy of elements in a period? Let’s use period 2 as an example: So the trend for ionization energy from left to right on the periodic table is… Why? – As the nuclear charge increases, the electrons are more strongly attracted, and more energy is needed to remove them from the atom. What can we say about the electronegativity trend in a period?

Trends in a Period 2. Atomic Radius - What happens to the atomic radius of elements in a period? Let’s use period 3 as an example: So, the trend for atomic radius from left to right on the periodic table is… Why? The valence electrons are all on the same energy level, but the number of protons in the nucleus increases, so the attraction towards the center of the atom is stronger. Therefore, the radius decreases.

Properties of Groups With few exceptions, each member of a group has the same number of valence electrons. Because the number of valence electrons determines the chemical reactivity of an element, members of a group have similar chemical properties.

Trends in a Group 1.Ionization Energy – What happens to the first ionization energy of elements in a group? Let’s look at group 1. So, the trend for the first ionization energy in a group from top to bottom is… Why? The valence electrons in each successive element are at a higher level so they are farther away from the nucleus. Therefore it is easier to remove them. What can we say about the electronegativity trend in a group?

Trends in a Group 2. Atomic Radius - What happens to the atomic radius of elements in a group? Let’s use group 7 as an example: So, the trend for atomic radius in a group from top to bottom is… Why? The elements from top to bottom have more energy levels to shield the valence electrons from the positive nucleus. Therefore, their attraction is lower.

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