Unit 2 Part 2: Periodic Trends

Transcription

1 Unit 2 Part 2: Periodic Trends

2 Outline Classification of elements using properties Representative elements, transition elements Metals, nonmetals and metalloids Classification of elements using electron configuration Valence electrons and period s, p, d, f blocks Periodic Trends Atomic radius, ionic radius Ionization energy Electronegativity

3 Classifying the Periodic Table: Using Physical and Chemical Properties Representative elements: groups 1-2 and Transition elements: groups 3-12 Elements are classified as metals, metalloids or nonmetals.

4 Classifying the Periodic Table: Using Physical and Chemical Properties Metals: Shiny Good conductors of electricity and heat Malleable: can be shaped into many shapes Ductile: can be drawn into wires

5 Classifying the Periodic Table: Using Physical and Chemical Properties Special metals: Group 1 elements are called alkali metals. They are very reactive. Eg. Group 2 elements are called alkaline earth metals. They are also very reactive. Eg.

6 Classifying the Periodic Table: Using Physical and Chemical Properties Transition metals: Transition metals: Groups 3-12 Inner transition metals: lanthanide series and actinide series.

7 Classifying the Periodic Table: Using Physical and Chemical Properties Nonmetals: Gas, solid, or liquid. Brittle Poor conductors of heat and electricity Eg. Group 17: Halogens Eg. Group 18: Noble gases

8 Classifying the Periodic Table: Using Physical and Chemical Properties

9 Classifying the Periodic Table: Using Physical and Chemical Properties Metalloids: Properties of both metals and non metals Eg. Silicon, Si:

10 Classifying the Periodic Table Using Electron Configuration Electron configuration determines the chemical properties of an element. Valence electrons are electrons in the highest principal energy level of an atom. Atoms in the same group have similar chemical properties because they have the same number of valence electrons. Eg. Group 1

11 Classifying the Periodic Table Using Electron Configuration Each of the representative groups (column in groups 1,2 and 13 to 18) has its own valence electron configuration. Valence electrons and period: The principal energy level of an element s valence electrons = the period of the periodic table that the element is in. Eg.

12 Classifying the Periodic Table Using Electron Configuration s-block, p-block, d-block, and f-block elements The periodic table has columns and rows of varying sizes. This is because the table has been divided into sections, or blocks, representing the valence electrons sublevels. (ie. s, p, d, or f)

13 Classifying the Periodic Table Using Electron Configuration 1. Which groups are the s-block elements? What do the valence electrons for these groups look like? Why are there only two groups in the s-block? 2. Which groups are the p-block elements? Why are there no p-block elements in period 1? Why are there six groups in the p-block? 3. What is a characteristic of the d-block? Example: Why are there ten groups in the d-block? 4. Which groups make up the f-block elements? Why are there 14 groups in the f-block?

14 Periodic Trends: Atomic Radius Many properties change in a predictable way. This pattern is called a trend. An atom s radius is defined by how close it can get to another atom. This is because an atom has no clearly defined edge.

15 Periodic Trends: Atomic Radius A metal atom s radius is defined as half the distance between neighboring nuclei in a crystal structure. A nonmetal s atomic radius is defined as half the distance between nuclei of identical atoms that are bonded together.

16 Periodic Trends: Atomic Radius The atomic radius decreases across a period. This is because of an increasing positive charge in the nucleus, and also because the principal energy level within a period remains the same. No additional electrons come between the valence electrons and the nucleus.

17 Periodic Trends: Atomic Radius The atomic radius increases down a group. Electrons are added to orbitals in higher principal energy levels =further from the nucleus. The orbitals between the nucleus and the outer electrons shield the outer electrons from the nucleus.

18 Periodic Trends: Atomic Radius P. 189 Q16-19

19 Periodic Trends: Ionic Radius Atoms can gain or lose electrons to form a charged version of itself, which is called an ion. When atoms lose electrons, they form ions called cations. When atoms gaim electrons, they from ions called anions.

20 Periodic Trends: Ionic Radius Atoms can gain or lose electrons to acquire a full set of eight valence electrons. This is called the octet rule. This is because the electron configuration of filled s and p orbitals of the same energy level is very stable. Exception: period 1 elements. They are complete with only two valence electrons.

21 Periodic Trends: Ionic Radius Positively charged ions: Smaller than the parent atom. Because: 1. The lost electron is a valence electron (in the outer shell) so the ion s radius is smaller than before. 2. Less electrostatic repulsion because there are fewer electrons. So the remaining electrons experience a greater pull to the positively charged nucleus.

22 Periodic Trends: Ionic Radius Negatively charged ions: Larger than the parent atom. Because: More electrostatic repulsion because there are more electrons, which forces them to move further apart. The increased distance between the outer electrons results in a larger radius.

23 Periodic Trends: Ionic Radius

24 Periodic Trends: Ionic Radius Across a period: Ionic radius decreases. Down a group: Ionic radius increases (electrons are in higher principal energy levels = bigger radius)

25 Periodic Trends: Ionization Energy Energy required to remove an electron from a gaseous atom. First ionization energy: Second ionization energy: High ionization energy means Low ionization energy means

26 Periodic Trends: Ionization Energy

27 Periodic Trends: Ionization Energy Across a period: ionization energies usually increase. Down a group: ionization energies usually decrease. Jump in ionization energies after all the valence electrons are removed.

28 Periodic Trends: Electronegativity The ability of an atom to attract electrons in a chemical bond.

29 Periodic Trends: Electronegativity Across a period: increases Down a group: decreases