Some observations from the final exam…

Review from Chapter 4 & 5 Can atoms of two different elements have the same ground state electron configuration? NO!!!! The number of protons is unique for each element, therefore an atom of that element has a unique number of electrons (atoms are neutral, p + = e - ) The electron configurations are different b/c different atoms have different number of electrons.

Review from Chapter 4 & 5 Write the electron configuration of the following: Argon: Calcium: Iron (Fe): Bromine (Br): 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 Core electrons [Ar] i.e., noble gas core Outer electrons – outside of the noble gas core Valence electrons

Ions Ions are atoms or groups of bonded atoms that have a positive or negative charge Ions are formed by losing or gaining electrons! an atom gains electron(s) and becomes a negative ion (anion) an atom loses electron(s) and becomes a positive ion (cation)

Review from Chapter 4 & 5 Metals vs. non-metals Ionization energy decreases (takes less energy to remove an electron) Electron affinity increases

Review from Chapter 4 & 5 Let’s look at electron configurations of ions… Argon: Argon is a noble gas. It’s valence shell has a stable octet (8 electrons). It will not form an ion because it already has an extremely stable electron configuration. 1s 2 2s 2 2p 6 3s 2 3p 6

Review from Chapter 4 & 5 What kind of ion would the following atoms form? Write the electron configuration of the ion. Argon: Calcium: Calcium will be more stable if it can achieve an electron configuration similar to Ar. To do so, it will form a cation, Ca 2+, by getting rid of its two valence electrons 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Ca 2+

Review from Chapter 4 & 5 What kind of ion would the following atoms form? Write the electron configuration of the ion. Krypton: Bromine (Br): Bromine has a high electron affinity. It is very close to having an octet in its valence shell. It will gain an electron to fill its valence shell and become an anion, Br -, and its electron configuration is the same as Kr. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 6 Br -

Review from Chapter 4 & 5 Transition metals and ions… Iron (Fe): Transition metals have 2 valence electrons. Many transition metals can form cations with different charges. When transition metals form ions, they will lose electrons from highest s sublevel first, then they may lose electrons from the d sublevel as well. We will talk more about transition metals later… 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6

Chapter 6 - Chemical Bonding Section 6.1 – Introduction to Chemical Bonding

Combinations Few elements exist as independent particles, most substances are made up of combinations of atoms held together by chemical bonds.

Chemical Bond A mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.

Why Atoms Bond to Other Atoms Most atoms are less stable existing by themselves (they are at a relatively high potential energy). Nature favors arrangements in which potential energy is minimized. Bonding creates more stable arrangements of matter in lower potential energy states. (Mama Nature doesn’t like to sweat!).

Bonding Valence electrons are redistributed. Three main types: Covalent Ionic Metallic Not male bonding!

Types of Chemical Bonding Ionic vs. Covalent Electrical attraction between cations and anions. Due to gain or loss of electrons (also called electron transfer) between atoms. Sharing of electron pairs between atoms H 2 H 2 O

Unique Covalent Bonding of C and Si Can form 4 covalent bonds. Can also bond with itself to form long-chain molecules of different sizes and shapes.

Metallic Bonding (not in text – yet) The attraction between metal atoms and the surrounding sea of electrons.

Bonding usually falls between ionic and covalent. This depends on how strongly the atoms of each element attract electrons. So we look at the electronegativity difference (atom x - atom y; F – Cs = 4.0 – 0.7 = 3.3). 0……..0.3…………….1.7………………3.3 nonpolar polar ionic covalent covalent ex. O 2 H 2 ONaCl (POLAR = uneven sharing of electrons.)

Non-polar Covalent A covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge. Example: Two hydrogen atoms combine to form H 2 gas.

Polar Covalent Bonds A covalent bond in which the bonded atoms have an unequal attraction for the shared electrons. Such bonds are polar, in that they have an unequal distribution of charge. Example: Hydrogen chloride HCL δ (Greek lower case delta) means “partial” δ−δ−δ+δ+

Rules for determining which type Electronegativity differences, or percentages of ionic character determine the bond type: (Electronegativity values for elements are on p.151) difference % Ionic> Polar C Non-polar <0.3 <5 covalent

Assignments – Due Wednesday BOP 6.1 Worksheet 6.1 Review Problems