Li or Na Li or Be Ar or Kr Al or Si

Transcription

1 Pre- AP Chemistry 11 Atomic Theory V Name: Date: Block: 1. Atomic Radius/Size 2. Ionization Energy 3. Electronegativity 4. Chemical Bonding Atomic Radius Effective Nuclear Charge (Z eff) Ø Net positive charge experienced by electrons Ø Affected by: (1) number of protons (2) number of shielding electrons Z eff = Z S Where Z = the number of S = the number of Ø Which atom has a greater effective nuclear charge? Li or Na Li or Be Ar or Kr Al or Si Shielding Effect Ø The balance between the pull of the on the valence electrons Ø The more shielding the further the valence shell can spread out and the bigger the atom will be. Draw the Bohr Diagrams for the following atoms: Sodium Magnesium Looking across a period is larger than and have the same number of shells has more protons and therefore has e- pull and the e- are held e- pull means. Sodium Potassium Looking down a family is larger than and have different number of shells has shells has shells shells means.

2 The size of an atom Ø The outer boundary of an atom depends on the size of a cloud in which electrons spend approximately % of their time. Ø The volume of an atom is the result of a of electrons. Ø What affects the size of an atom s electron cloud? Consider this Rank the following from largest to smallest: How many electrons are in each? How many protons are in each? Al 3+ F - Mg 2+ N 3- Na + Ne O 2-

3 Ionization Energy Ionization Energy: The required to remove an electron from a neutral atom. IE value tells us how strongly an atom holds onto its outermost electrons. Let s compare atoms of different sizes Small Atomic Radius Large Atomic Radius Electrons are held tightly Requires a lot of energy to remove a valence electron Electrons are held less tightly Requires less energy to remove a valence electron Higher ionization energy Lower ionization energy Practice: Rank the following list of elements in order of decreasing ionization energy: Aluminum Argon Cesium Magnesium Rubidium Silicon Sodium Sulphur

4 Electronegativity Attracting electrons in general: Called. Attracting electrons in a bond: Called. Each atom has a specific value electronegativity means electron density. When a bond is formed, the positive is attracted to the negative of the other atom. Let s compare atoms of different sizes Small Atomic Radius Large Atomic Radius Less e- shielding around the nucleus Protons in the nucleus can easily attract electron from the other atom Higher effective nuclear charge (Z eff) More e- shielding around the nucleus Protons in the nucleus are shielded by electron cloud Lower effective nuclear charge (Z eff) Higher electronegativity Lower electronegativity Practice: Rank the following list of elements in order of decreasing electronegativity: Aluminum Argon Cesium Magnesium Rubidium Silicon Sodium Sulphur

5 Summary Decreases or increases? Moving LEFT to RIGHT Across A Period Moving DOWN a Chemical Family Atomic Size Reason: Ionization Energy Reason: Electronegativity Reason: Fill in the arrows with the following terms: Increasing atomic radius Increasing ionization energy Decreasing atomic radius Decreasing ionization energy Increasing electronegativity Decreasing electronegativity

6 Chemical Bonding Ionic Bonding Atomics Involved in Chemical Bond Type of Chemical Bond 1. metal bonded to non- metal Ionic bond 2. non- metal bonded to non- metal Covalent bond 3. metal bonded to metal Metallic bond Electrostatic attractive force between the oppositely charged ions produced when a metal atom transfers one or more electrons to a non- metal atom. Important Points: 1. Ionic compounds form between and whose ΔEN exceed. They typically form when metals from groups 1 or 2 react with non- metals from groups 16 or 17 of the periodic table. 2. During the formation of an ionic bond, metal atoms will one or more electrons to the more non- metal atoms. This occurs because the metal s relatively low and. 3. Ionic compounds form structures known as. The vast number of attractive forces present in such lattices account for the high melting temperatures of ionic compounds. Problems: Write formulas for the compounds formed when the following elements combine and justify that the bonds present are ionic by determining the ΔEN in each case. a) Ca and Br b) Al and O c) Be and O d) Rb and N e) Ba and Cl Practice 1: Write formulas for the ionic compounds form when the following elements combine: a) Ba and Br b) Be and O c) Sr and N d) Mg and Cl e) Fr and F Practice 2: Justify that the bonds in the following compounds are ionic by calculating the ΔEN values for each. a) RbF b) NaCl c) RaCl 2 d) KBr e) Na 2O

7 Covalent Bonding Electrostatic attractive force between the oppositely charged ions produced when a metal atom transfers one or more electrons to a non- metal atom. Important Points: 1. Covalent compounds form between two. 2. Because no electron transfer occurs and no ions form, all of the species prior to and following covalent bond formation between two atoms are electrically. 3. The force of attraction in a covalent bond is between a pair of and two adjacent positive, rather than between a cation and an anion. Electrons in covalent bonds are always associated in pairs. 4. Covalent compounds exist as independent molecules rather than large crystal structures. ΔEN Bond Designation Problems: Write formulas for the compounds formed when the following elements combine and justify that the bonds present are covalent by determining the ΔEN in each case. a) N and F b) C and H c) Si and N d) C and S e) O and O Practice 1: Calculate the ΔEN values for the bonds in the following compounds. Then arrange the compounds in order from those containing bonds in which the electrons are shared most equally to those in which the electrons are shared most unequally. a) H 2O b) PCl 3 c) Cl 4 d) SiO 2 e) AlN

8 Practice 2: Complete the following table: Elements Present Formula ΔEN values Nature of Bonds Atom Possessing Greater Electron Density C and S B and Cl Al and O N and I Ca and F Practice 3: Determine the type of bonds present in the following compounds: F Li Be B C N O F Cl Na Mg Al Si P S Cl Br K Ca Ga Ge As Se Br Does every metal & non- metal combination result in an ionic bond?