Unit 3 Periodic Table

1. Unit 3 Periodic Table James Hutchison ROHS

2. Development of the Periodic Table • By the mid-1800s, about 70 elements were known • Dmitri Mendeleev ordered the elements in columns in order of increasing atomic mass in the very 1st periodic table • In 1913, Henry Moseley determined the atomic number of atoms of elements, and used increasing atomic number to re-order the periodic table. It still stands today.

3. The Modern Periodic Table • The horizontal rows are known as periods • There are 7 periods • Properties of elements change as you move across each period • Gives rise to the periodic law • When elements are arranged in increasing atomic number, there is a periodic repetition of their physical and chemical properties • The vertical columns are called groups • There are 18 groups, or families • Elements in groups have similar physical and chemical properties

4. Groups are given a number and a letter • The letters, A and B, signify properties • Group A elements are called the representative elements because they exhibit a wide range of physical and chemical properties • Group B are the transition elements

5. 8A 1A 2A 3A 4A 5A 6A 7A • Elements in the 1A-7A groups are called the representative elements outer s or p filling

6. These are called the inner transition elements, and they belong here The group B are called the transition elements

7. The periodic table consists of 3 main types of elements: metals, non-metals and metalloids • Metals • Make-up 80% of all elements • High heat and electrical conductivity • High luster, ductility and malleability • Alkali metals, alkaline earth metals (Gr.A) • Alkali Metals are the metals in Group 1A • Alkaline Earth Metals are in Group 2A • Transition metals and inner transition metals (Gr.B) • Inner transition metals are also called rare-earth metals

8. H Group 1A are the alkali metals (but NOT H) Group 2A are the alkaline earth metals

9. Non-metals • Upper right corner of the periodic table • Poor conductors • Low luster, ductility and malleability • Many exist as gases at room temperature • Two Special groups: Halogens & Noble Gases • Halogens are in Group 7A • Noble Gases called inert gases are in Group 0 or 8A

10. Group 8A are the noble gases • Group 7A is called the halogens

11. Metalloids • Consists of elements with properties that are intermediate between those of metals and non-metals

13. Periodic TRENDS • Ionization energy • The energy required to overcome the attraction of the nuclear charge and remove an electron from a gaseous atom is the ionization energy • The first ionization energy generally decreases as you move down a group • Electronegativity • Electronegativity is the tendency for an atom to attract electrons when they are chemically combined with atoms of another element • Measured in units of Paulings • Electronegativity generally decreases as you move down a group • As you move across a period from left to right, electronegativity of the representative elements increases

14. The arrows indicate the trend: Ionization energy and Electronegativity INCREASE in these directions

15. Trends in atomic size • Atomic radius is ½ the distance between the nuclei of two like atoms in a diatomic molecule • Atomic radius indicates relative size (usually measured in picometers) • Atomic size usually increases as you move down a group • Electrons are added to successively higher energy levels • The shielding of the nucleus by electrons increases (shielding effect) • Overcomes the shrinking effect caused by the increasing charge of the nucleus

16. Trends in ionic size • Atoms of metallic elements have low ionization energies and they form positive ions easily • Atoms of non-metallic elements readily form negative ions • The loss or gain of electrons affects the size of the ions formed • Going from left to right across a period, there is a gradual decrease in the size of positive ions (cations) • Beginning with Group 5A, the negative ions (anions) gradually decrease in size as you continue to move right • The ionic radii of both cations and anions increase as you move down a group

17. Atomic size and Ionic size increase in these directions:

18. Electron Affinity • The electron affinity is a measure of the energy change when an electron is added to a neutral atom to form a negative ion.