Bond

Day 2: #4

Chemical Bond

Day 2: #4

Before there were bonds, there had to be elements!

Let’s review elements & the Periodic Table

THISTABLE:

No, not that table –

Day 2: #4

What are Chemical Bonds?

• An attraction between two or more atoms

• Interaction between valence electrons

• All atoms need 8 valence electrons to be “happy” or stable

Day 2: #4

Two Kinds• Ionic Bonds

– Form Ionic compounds – (by losing /gaining electrons)

• Covalent Bonds– Form Covalent compounds– (by sharing electrons; “Co” means to share)

Day 2: #4

How Do Ionic Compounds Form?

• metals (from groups 1,2,3 on the Periodic Table) combine with nonmetals (from groups 17, 16, 15).

Day 2: #4

How Do Ions Form?…by losing or gaining - electrons

• Positive ions form, when valence electrons are lost

(result = more + protons than – electrons which makes the charge +)

Metals lose electrons, therefore:

Group 1 metals: become +1 ions

Group 2: +2 ions

Group 3: +3 ions Day 2: #4

Lets look at Sodium to see how this is so …

• Sodium has 11 protons; 1 valence electron

• It is easier for Sodium to lose an electron to “be happy.”

11 p+

11 e-neutral

11 p+

10 e-

cation

0+1 charge for sodium (Na) Day 2: #4

Ions can be negative too!

• Negative ions form when electrons are gained.

(result = more - electrons than + protons which makes the charge -)

Nonmetals gain electrons, therefore

Nonmetals from

Group 15: become - 3 ions

Group 16: - 2 ions

Group 17: - 1 ions Day 2: #4

Lets look at Oxygen• Oxygen has 8

protons; 6 valence electrons

• It is easier for oxygen to gain two electrons to “be happy.”

8 p+

8 e-

0

neutral

8 p+

10 e-anion

O

- 2 charge for oxygen (O)

Day 2: #4

…but how do ions BOND?

For ions the “bonding” refers to the giving and taking of electrons

The result is an ionic compoundExample:sodium (Na) gives 1 e and

chlorine (Cl) takes it

Na (+1) Cl (-1) NaCl

Day 2: #4

How do COVALENT bonds form?

• nonmetals (from groups 17, 16, 15) share valence electrons in order to obtain 8 total valence electrons and be “happy”

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How do nonmetals share?

The sharing of electrons is either equal or unequal.

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Unequal sharing (polar covalent)

Equal sharing (nonpolar covalent)

Sharing to obtain 8 valence electrons….how does that look?

Day 2: #4

C is in group 14 and has 4 valence electrons. Cl is in group 17 and has 7 valance electrons. By sharing, the C and each Cl is able to have 8 valence electrons!

An unidentified element has many of the same

physical and chemical properties as

magnesium and strontium but has a lower

atomic mass than either of these elements.

What is the most likely identity of this

element?

 

F Sodium

G Beryllium

H Calcium

J Rubidium

Day 2: #4Question from TEA released TAKS test

The elements of which of these groups on the periodic table are most resistant to forming compounds?

 

A Group 1

B Group 9

C Group 14

D Group 18

Day 2: #4Question from TEA released TAKS test

The elements from which of the following

groups are most likely to react with

potassium (K)?

 

F Group 2

G Group 7

H Group 13

J Group 17

Day 2: #4Question from TEA released TAKS test

Which of the following groups contains

members with similar chemical reactivity?

 

A Li, Be, C

B Be, Mg, Sr

C Sc, Y, Zr

D C, N, O

 

Day 2: #4Question from TEA released TAKS test

According to the periodic table, which element most readily accepts electrons?

 

A Fluorine

B Nitrogen

C Arsenic

D Aluminum  

Day 2: #4Question from TEA released TAKS test

Law of Conservation of MassMatter cannot be created or destroyed in an

ordinary chemical reaction.

To show this all chemical equations must be balanced! When balancing an equation only

coefficients can be added or changed. Subscripts cannot be changed!

Example: 2NaCl → 2Na + Cl2

The 2’s in front of NaCl and Na are coefficients. The 2 below Cl is a subscript.

Day 2-#3

Which chemical equation supports the law of conservation of mass?

F 2H2O(l) → H2(g) + O2(g)

G Zn(s) + HCl(aq) → ZnCl2(aq) + H2(g)

H Al4C3(s) + H2O(l) → CH4(g) + Al(OH)3(s)

J CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

(All practice problems are from TEA released TAKS Tests)Day 2-#3

Counting Atoms

Name and Use Formula Atoms in Formula

Silicon Dioxide

Use: Sand

SiO2 Si = Silicon 1

O = Oxygen 2

Calcium dihydrogen phosphate

Use: fertilizer

Ca(H2PO4)2

Ca=Calcium 1

H = Hydrogen 4

Phosphorous = 2

Oxygen = 8

Practice Problems: (All practice problems are from TEA released TAKS Tests)

What are the coefficients that will balance this chemical equation?

A 2, 1, 1

B 3, 4, 2

C 2, 2, 1

D 4, 3, 2

Day 2-#3

What is the coefficient for H2O when the above equation is balanced?

A 1

B 2

C 3

D 4

(All practice problems are from TEA released TAKS Tests)Day 2-#3

According to this information, what is the chemical formula for aluminum sulfate?

A AlSO4

B Al2(SO4)3

C Al3(SO4)2

D Al6SO4

(All practice problems are from TEA released TAKS Tests)Day 2-#3

The chemical equation shows CaCO3 being heated. Which of these statements best describes the mass of the products if 100 g of CaCO3 is heated?

A The difference in the products’ masses is equal to the mass of the CaCO3.

B The sum of the products’ masses is less than the mass of the CaCO3.

C The mass of each product is equal to the mass of the CaCO3.

D The sum of the products’ masses equals the mass of the CaCO3.

(All practice problems are from TEA released TAKS Tests)Day 2-#3

The chemical formula for calcium chloride is —

F Ca2Cl

G CaCl

H CaCl2J Ca2Cl3

(All practice problems are from TEA released TAKS Tests)Day 2-#3

When 127 g of copper reacts with 32 g ofoxygen gas to form copper (II) oxide, no copper or oxygen is left over. How much copper (II) oxide is produced?

F 32 gG 95 gH 127 gJ 159 g

(All practice problems are from TEA released TAKS Tests)Day 2-#3

When the above equation is balanced, the

coefficient for magnesium chloride is —

A 0

B 1

C 2

D 4

(All practice problems are from TEA released TAKS Tests)Day 2-#3

According to the law of conservation of mass, how much zinc was present in the zinc carbonate?

A 40 gB 88 gC 104 gD 256 g

(All practice problems are from TEA released TAKS Tests)Day 2-#3

Elements in Group 16 of the periodic table

usually —

 

F form large molecules

G gain electrons when bonding

H act like metals

J solidify at room temperature

Day 2: #4Question from TEA released TAKS test