Chem Ch 3

Classify the bonds formed between each pair of elements based on electronegativity values in the following table: (see picture) Keep in mind: Ionic is or more 1.9 Polar is 0.5 to 1.8 Non-polar is 0 to 0.4

Ionic: Be-F, Sc-O Polar: H-Br, S-O, Be-Cl Non-polar: S-I, H-P, P-Se Beryllium, Be, is an element that can form covalent compounds even though it is a metal. BeCl2 is a common example of a metal-nonmetal combination that is covalent rather than ionic in the gas phase, and behaving more like a metalloid in the solid phase. For a P−Se bond, a H−P bond, and a S−I bond, the electronegativity difference is less than 0.4 and so these bonds are essentially nonpolar covalent. Using electronegativity values rather than just position on the periodic table is a more exact method of predicting bond type.

Arrange the bonds Si-S, F-Fe, and N-Cl in order of increasing covalent character.

F-Fe, Si-S, N-Cl Based on the difference in electronegativity the N-Cl bond is the least polar, and the F-Fe bond is the most polar.

Naming Binary Molecular Compounds

Molecular compounds are usually composed solely of nonmetals. A binary molecular compound is one in which the compound contains only two elements (regardless of how many atoms are present of each). When naming binary molecular compounds, prefixes are used to specify the number of atoms of each element. Take a moment to review some of the prefixes shown here. For example, SF6 is named sulfur hexafluoride. Note that the prefix mono is not used in naming the first element. Also note that the second element in the name should end with the suffix ide.

Which of the following statements about electronegativity is INCORRECT?

When elements with very different electronegativity values form compounds, they form covalent compounds.

Give systematic name for the following compound: (see picture)

dinitrogen monoxide

N₂O₅

dinitrogen pentoxide

What is the name of the covalent compound N₂O₅?

dinitrogen pentoxide

N₂O₃

dinitrogen trioxide

A probe sent to the planet Mercury has measured the electronegativities of several elements it has detected on the planet. Which element would you expect to identify as a metal?

element 2 The element with an electronegativity value of 1.88 is cobalt (Co), which is indeed a metal. Boron (χ=2.04) is a semimetal, and iodine (χ=2.66), selenium (χ=2.55), and oxygen (χ=3.44) are nonmetals.

Atomic Radius

Atomic radius is one periodic property of the elements. Atoms become smaller from left to right across a row, but they become larger going down a column. The largest atoms are thus found in the bottom left corner of the periodic table.

Carbon tetrafluoride

CF₄

What is the formula for the compound methane?

CH₄

Carbon tetraiodide

CI₄

Which of the following substances are nonpolar covalent? BaCl2 Cl2 BrF3 NH3 CdBr2 PCl3 CsI MgO

Cl₂

What general trends in electronegativity occur in the periodic table?

Electronegativity increases from left to right across a period and decreases down a group.

Electronegativity

Electronegativity is another periodic property. An atom's electronegativity describes its ability to attract electrons to itself when it is part of a chemical compound. Electronegativity increases diagonally from the lower left to the upper right of the periodic table. Highly electronegative elements (with a chi value of χ≥2.2) are insulating nonmetals, whereas elements with low electronegativity (with χ≤1.8) are conducting metals.

Iodine monochloride

ICl

Ionization energy

Ionization energy is another periodic property of the elements. The ionization energy of an atom is the energy required to remove an electron when the element is in a gaseous state. Ionization energies tend to increase from left to right across the row, but they decrease going down a column. The highest ionization energies are thus found in the upper right corner of the periodic table. Some sample ionization energies are shown in the table below.

Place the following elements in order of decreasing atomic radius: chlorine (Cl), lead (Pb), aluminum (Al), and fluorine (F).

Largest: Pb,Al, Cl, F :smallest

Naming Covalent Compounds

Many covalent compounds have common names that are not related to their chemical formula. However, systematic names for the compounds can be determined from the chemical formula of the compound by using an agreed-upon naming conventions.

Which of the following substances are largely ionic? PCl3 BrF3 CdBr2 MgO Cl2 BaCl2 NH3 CsI

MgO, BaCl₂, CsI

Order the following elements according to decreasing electronegativity:

Most electronegative: Br, I, Pb, Zn, Sr, Cs :Least electronegative

Nitrogen triiodide

NI₃

What is the formula for the compound nitrogen monoxide?

NO

A Venus probe detects an element with a first ionization energy of 2088 kJ/mol. Given the table of known ionization energies provided in the introduction, what is the most likely identity of this element Fe Rb Ne Hg

Ne

Which of the following formulas and names match? 1. N2O3 - dinitride trioxide 2. AsBr5 - arsenic pentabromide 3. Cl2O7 - dichlorine hexoxide 4. SiO2 - silver dioxide

Only 2 (AsBr5 - arsenic pentabromide)

Which of the following substances are polar covalent? BaCl2 MgO CsI PCl3 NH3 BrF3 Cl2 CdBr2

PCl₃ NH₃ BrF₃ CdBr₂

Phosphorus pentachloride

PCl₅

What is the name for the compound PCl₅?

Phosphorus pentachloride

Sulfur dioxide

SO₂

Disulfur diiodide

S₂I₂

Tetrasulfur tetranitride

S₄N₄

Covalent Compound Formulas

The chemical formula of covalent compounds can be easily determined from the systematic name of the compound. Greek prefixes are used to indicate the number of atoms of each element present in the compound.

Periodic Trends of the Elements

The periodic table is an organized listing of all the known elements. The table displays elements in order of their atomic number and groups them in vertical and horizontal rows that indicate similar properties. Several properties of atoms are periodic, meaning that the trends repeat themselves from row to row. This gives the periodic table its predictive value. In fact, several elements were predicted to exist before they were actually discovered, because there seemed to be gaps when the known elements were first accurately grouped into a periodic table

Consider the following element combinations. Classify the bonds formed between each pair as ionic, polar covalent, or nonpolar covalent based solely on each element's position on the periodic table.

Using the elements' positions on the periodic table is only a general tool to predict probable bond type. A more exact prediction of bond type can be made using electronegativity values.

An electrostatic potential map of water is shown. a. Which atom, H or O, is positively polarized (electron-poor)? b. Which atom, H or O, is negatively polarized (electron-rich)? c. Is this polarity pattern consistent with the electro-negativity values of O and H given in Figure 5.4 in the textbook?

a. H b. O c. yes

Which of the following substances are largely ionic, and which are covalent? a. HF b. HI c. PdCl₂ d. BBr₃ e.NaHO: Na⁺ - OH⁻ f. NaOH: OH⁻ g. CH₃Li

a. polar b. polar c. polar d. polar e. ionic f. polar g. polar

What is the name of the covalent compound CCl₄?

carbon tetrachloride

Cl₂O₇

dichlorine heptoxide

A covalent bond ____.

involves the force produced when valence electrons are attracted to two nuclei

Give systematic name for the following compound: (see picture)

phosphorus pentachloride

SeO₃

selenium trioxide

SiO₂

silicon dioxide

NaF

sodium fluoride

SF₆

sulfur hexafluoride

What is the name for the compound P₄O₁₀?

tetraphosphorus decoxide

P₄O₆

tetraphosphorus hexoxide

Dicarbon monoxide

C₂O

Adrenaline, the so-called "flight or fight" hormone, can be represented by the following ball-and-stick model. (see picture) What is the chemical formula of adrenaline? (gray = C, ivory = H, red = O, blue = N) Express your answer as a chemical formula. List the element symbols in alphabetical order.

C₉H₁₃NO₃

What is the formula for the compound tetraphosphorus decoxide?

P₄O₁₀

Which element has the highest (most negative) electron affinity? He S K Ba Cr

S

Electron affinity

The electron affinity of atoms is also periodic. The electron affinity of an atom is the energy that is lost or gained when an electron is added to a neutral atom of the element in a gaseous state. A more negative electron affinity is considered a higher electron affinity value. It tends to become more negative going from left to right across a row in the table and less negative going down a column. Electron affinities are not as smoothly periodic as some of the other properties, with some major exceptions opposing the general trends. For example, the group 2 and group 18 elements have positive electron affinities, and each of the row 2 elements B through F are less negative than the elements just below them in the column. In general, however, electron affinities tend to be more negative as you move toward the upper right-hand corner of the periodic table.

Covalent, Polar Covalent, and Ionic Bonds

When two bonded atoms attract electrons with equal strength, the result is a nonpolar covalent bond. A polar covalent bond is one in which the electrons are unequally shared between the atoms. An ionic bond results when the sharing is so unequal that fully charged ions form. Electronegativity difference can be used to predict bond type. One method to classify bonds based on this difference can be described as follows. If the electronegativities differ by less than 0.4 units, the bond can be classified as nonpolar covalent. If the difference is between 0.4 and 2.0 units, the bond is classified as polar covalent, and if the difference is more than 2.0 units, the bond is substantially ionic. If you are not given electronegativity values, you can still predict the bond type using the periodic table. Metals have low electronegativity compared to nonmetals. So in general, we can predict that any metal-nonmetal combination will be ionic and any nonmetal-nonmetal combination will be covalent. If electronegativity values aren't given, you should assume that a covalent bond is polar unless it is between two atoms of the same element.

Show the direction of polarity for each of the covalent bonds in each of the following compounds using the δ+/δ− notation. a. C−H b. C-Cl c. Si-Li d. Si-Cl e. N-Cl f. N-Mg

a. δ⁻C−Hδ⁺ b. δ+C−Clδ− c. δ−Si−Liδ+ d. δ+Si−Clδ− e. δ+N−Clδ− f. δ−N−Mgδ+