Test Answers on chemistry – Flashcards

Iodine, hydrogen, nitrogen, bromine, oxygen, chlorine and fluorine

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i have no bright or clever friends

to be polar a molecule must have polar bonds and be asymmetrical.

water h₂o ,

ammonia NH₃

and hydrogen chloride HCl are all polar molecules.

The atomic size decreases going across a period. the atomic raidius increases from the top to the bottom of a group.

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If it is an ion with a positive charge then it will be bigger compared to the pure element. if it is an ion with a negative charge then it will be smaller, becase it would have;gained electrons.

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therefore less valence electrons the;bigger;the;radius.

1. Na₂ O
2. AlBr₃

1. magnesium chloride
2. Potassium phosphide

1. (ClO₃)^-;;; Chlorate ion
2. (NO₃)^- nitrate ion
3. (CO₃)^2- carbonate ion
4. (PO₄)^3- Phosphate ion
5. (SO₄)^2- Sulfate ion
6. (NH₄)⁺ Ammonium Ion
7. (OH)^- hydroxide ion

Ionic compounds occur between metals and non metals.

However,; atoms of nonmetals share valence electrons and form covalent compounds.

• covalent bond - electrons are shared by atoms of 2 nonmetals (octet)
• nonpolar covalent bond - electrons are shared equally
• polar covalent bonds, electrons are unequally shared due to thier attraction to the more electronegative atom.
• some covalent compounds double or triple bnds are needed to provide an octet.
• the ending of the second nonmetal is changed to ide.

• EN is the ability of an atom to attract shared pairs of e-. The EN values of the metals are low, while nonmetals have high EN.
• in polar covalent bonds, the atom w the lower EN is partially positive adn the atom with the higher EN is partially negative.
• atoms that form ionic bonds have large differences in EN

• Ionic bonds consist of very strong attractivce forces between oppositely charged ions.
• attractive forces in polar covalent bonds are weaker than ionic bondsand include dipole-dipole attractions and hydrogen bonds.
• nonpolar covalent compounds form solids using temporary dipoles called dispersion forces.

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attractive forces between opposiely charged ends of polar molecules

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a polar covalent bond that has a separation of charges is called a dipole

it indicates the number and kinds of ions that make up the ionic compound. the sum of the ionic charges in the formula is always zero

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note: that the ionic charges of the ions do not appear in the formula of the ionic compound.

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the cation is always written first followed by the anion

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• the metal ion is named first follwed by the name of the nonmetal ion.
• subscripts are never mentioned; they are understood as a result of the charge balance of the ions in a compound
• ex. Mg²⁺Br^- =MgBr₂

because they lose their outer electrons as well as electrons from a lower energy level.

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when a metal can form two or more ions, it is not possible to predict the ionic charge from the group number. we say that is has a variable valence.

to do this, a Roman numeral that matches the ionic charge is placed in parentheses afer the elemental name of the metal.

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zinc, cadmium and silver only form one ion.

it depends upon the calculation of the ionic charge of the trasition metal in the formula.

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ex. Cu₂S

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step 1: determine the charge of the cation from the anion. the nonmetal S in Group 6A forms the S^2-, the charge of each Cu ion is 1+

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Metal:;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;Nonmetal

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Element: Copper;;;;;;;;;;;;;;;;;;;;;;;;;;;; Sulfur

Group: Transition;;;;;;;;;;;;;;;;;;;;;;;;;;;;6A

Ions: Cu ?;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; S^2-

Charge balance: 2(1+);;;;;;;;;+;;;;;;;;;;(2-) = 0;

Ions: Cu^{+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;} S^2-

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step 2: name the cation by its element name, and use a roman numeral in parentheses for the charge

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copper(I)

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Step3: Name the anion by changing the last part of it's element name to ide.

sulfide

Step 4: write the name of the cation first and the name of the anion second.

copper(I)sulfide

an ionic compound with 3 or more elements contais some type of polyatomic ion, which is a group of atoms that has an ionic charge. most polyatomic ions consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrgen bonded to oxygen atoms. these polyatomic ions have ionic charges 1-,2- or 3- because 1,2,3 electrons were gained by the atoms in the group to complete thier octets.

only one of the polyatomic ions is positively charged NH₄⁺

the names of most polyatomic ions end in ate.

 the ite ending is used for the names of related ions that have one less oxygen atom.

we follow the same rules of charge balance that we used for writing the formulas of simple ionic compounds. the total negative and positive charges must equal 0.

when more than one polyatomic ion is needed for charge balance, parentheses are used to enclose the formula of the ion. a subscript is written outside the closing parenthesis to indicate the number of polyatomic ions.

first write the positive ion, usually a metal, and then write th name of the polyatomic ion.

remember that other ionic compounds don't use prefixes.

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

because several different compounds can be formed from the same two nonmetals. for example, carbon; and oxygen can form two different compounds, carbon monoxide CO and carbon dioxide CO₂

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- When vowels o and o

and

a and o

appear together, the first vowel is omitted as in corbon monoxide

step 1: write the symbols in order of the elements in the names.

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B;;; O

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Step 2 : write prefixes as subscripts.

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B₂O₃

values increase from left to right across each period as well as from the bottom to the top of each group.

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there are no electronegativity values for the noble gases because they do not typically form bonds.

under .5 nonpolar covalent bond

.5 to 1.7 polar covalent bond

1.7 and up is ionic bond

ionic

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eventually the difference in electronegativy is great enough that electrons are transferred from one atom to another, which results in an ionic bond.

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nonpolar compounds do form solids, but at low temperatures. very weak attractions called dispersion forces occur between nonpolar molecules.

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disstriubted symmetrically

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form liquids and solids

Chemical changes                     Physical changes

rusting nail                           melting ice

bleaching a stain                   boiling water   

burning a log                        sawing a log in half

tarnishing silver                    tearing paper

fermenting grapes                 breaking a glass

souring of milk                     pouring milk

a chemical reaction alwasy involves chemical change as bonds between the atoms in the original substances are broken and new bonds are formed.

during a chemical change, new properties become visibly, which are clues that tell you a chemical reaction has taken place

change in colour

formation of gas (|bubbles)

formation of a solid (precipiate)

heat (or a flame) produced by heat absorbed

Equation:     C(s) + O₂(g) ----> CO₂ (g)

                     Reactants                   Product

NO,

every reaction must be showed as a balanced equation, which shows the same number of atoms for each element on both sides of the arrow.

in a combination reaction, two or more elements or compounds bond to form one product.

 for example, sulfur and oxygen combine to form the product sulfur dioxide.

S(s) + O₂(g) ----> SO₂(g)

in a decomposition reaction, a reactant splits into two or more simpler products.

 for example when mercury(II)oxide is heated, the compound breaks apart into mercury atoms and oxygen.

           heated

2HgO(s) ----> 2Hg(l) + 0₂(g)

in a replacement reaction, elements in a compound are replaced by other elements.

a reacting element switches places with an element in the other reacting compound.

A    +    BC  ----->   AC   + B

                   One element                  replaces                 another element

the positive ions in the reacting compounds switch places.

AB + CD    ---------> AD + CB

                Two elements                   replace each other

1. Single replacement reaction
2. decomposition
3. double replacement reaction

To determine oxidation and reduction, we need to look at ions and charges in the reactant. in AgBr, there is a silver ion

Ag⁺ with a 1+ charge and a bromide ion (Br^-) with a charge of 1-. we can write the reaction as follows:

2Ag⁺(aq) + 2Br^-(aq) ------>2Ag(s) + Br₂(g)

now we can compare Ag⁺ with the product Ag atom. int his case, each Ag⁺ gained an electron, which is reduction.

2Ag⁺(aq) + 2e-----> 2Ag(s) reduction

then we compare the Br^- with the Br iin the product Br_2. In this case, each Br^- lost an electron, which is oxidation.

2Br^-(aq) -----> Br₂(g) + 2e^-  oxidation

in this reaction , bromide ion is oxidized and silive ion is reduced.

is a group of atoms

has an overall ionic charge

• occurs between nonmetals
• is an equal or almost equal sharing of electrons
• has almost no electronegativity difference 0.0 - 0.4

• occurs between nonmetal atoms
• is an unequal sharing of electrons
• has a moderate electronegativity difference .5 to 1.7

• occurs between metals and nonmetals
• is a result of electron transfer
• has a large electronegativity difference 1.8 or more

• ionic compounds requare large amounts of energy to break apart ionic bonds. thus, they have high melting points.
• hydrogen bonds are the strongest type of dipole-dipole attractions. they require more energy to break than other dipole-dipole attractions.
• dispersion factors are weak interactions and very little energy is needed to change state.