A huge science question!!!?

Question

Compare the three types of bonds, ionic bond, metallic bond, and covalent bond based on what happens to the valence electrons of the atoms.

Please help!

Answer 1

here is a bunch of wiggy waggy hope it helps

UNIT 3: BONDING

The chemical forces of attraction that hold atoms or ions together in chemical compounds are called chemical bonds. All chemical bonds result from the simultaneous attraction of one or more electrons by two or more nuclei.

There are three types of bonds: Ionic, Covalent and Metallic.

3.1 Ionic Bonding

Ionic bonding requires a transfer of electrons from a metal to a nonmetal, a process that forms ions. An attractive force exists between the oppositely charged ions, called electrostatic attraction. The force that keeps the ions held together is the chemical bond called the ionic bond.

http://ithacasciencezone.com/chemzone/lessons/03bonding/mleebonding/ionic_bonds.htm

Example: Ionic Bonding in Sodium Chloride

A sodium atom loses its topmost energy level electron to become a sodium ion (cation).



A Cl2 molecule gains two electrons to become two chloride ions, (anions).




Combining the above processes, the overall effect is the transfer of ONE electron from sodium to chlorine.



The oppositely charged sodium and chloride ions attract each other and ionic bonds are formed.

In the solid state, each cation is surrounded by anions, and each anion is surrounded by cations. These ions arrange themselves in a 3-dimensional crystal.

Properties of Ionic Compounds


The strong attractions between the cations and the anions in ionic solids are responsible for their high melting points. For ionic compounds, melting points typically range from 300°C to 1000°C.
Ionic compounds are soluble in water.
In aqueous solution, an ionic compound dissociates into its ions.
This means that when NaCl is dissolved in water, the solution contains Na+ ions and Cl ¯ ions.
http://ithacasciencezone.com/chemzone/lessons/03bonding/dissociate.htm

The dissociated ions in aqueous solution give the solution the ability to conduct electricity.


3.2 Covalent Bonding

The chemical bonds formed by sharing of electrons between non-metals elements are referred to as covalent bonds. The location of an element in the periodic table allows us to predict the number of covalent bonds that it can form.

1. Group IA elements all have 1 valence electron: e.g. Hydrogen has one valence electron, shares this valence electron with another atom to form one covalent bond
2. Group IIA elements all have 2 valence electrons: e.g. Beryllium has two valence electrons, shares its valence electrons with other atoms to form two covalent bonds.
3. Group IIIA elements all have 3 valence electrons: e.g. Boron has three valence electrons, shares its valence electrons with other atoms to form three covalent bonds.
4. Group IVA elements all have 4 valence electrons: e.g. Carbon has four valence electrons, shares its valence electrons with other atoms to form four covalent bonds.
5. Group VA elements all have 5 valence electrons:e.g. Nitrogen has five valence electrons, shares three of its five valence electrons with other atoms to form three covalent bonds. The other two valence electrons form one nonbonding electron pair.
6. Group VIA elements all have 6 valence electrons: e.g. Oxygen has six valence electrons. These elements need two valence electrons to complete an octet of electrons. They share two of the six valence electrons with other atoms to form two covalent bonds. The other four valence electrons form two non-bonding electron pairs.
7. Group VIIA elements all have 7 valence electrons: e.g. Fluorine, Chlorine, Bromine and Iodine each have seven valence electrons. These elements need one valence electron to complete an octet of electrons. They share one of the seven valence electrons with other atoms to form one covalent bond. The other six valence electrons form three non-bonding electron pairs.
8. Group VIIIA elements all have 8 valence electrons.



When a covalent bond is formed between two identical non-metals, a non-polar covalent bond is formed. In total, there are seven elements that exist as diatomic molecules. These are the diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2.

http://ithacasciencezone.com/chemzone/lessons/03bonding/mleebonding/covalent_bonds.htm


When electrons in a bond are shared unequally, the bond is called polar covalent bond or polar bond.

Lewis structure of covalent molecules

When electrons are shared between two atoms, one atom donates one electron and the other atom donates the second electron. The shared pair of electrons representsa covalent bond.

If two pairs of electrons are shared between two atoms, a double bond exists. When two atoms share three pairs of electrons, a triple bond exists.

The sharing of electrons follows the same basic principle as prevails in the formation of ions. This fact means that the atoms are seeking to attain noble-gas electronic configurations.

The 'Octet Rule' states that the noble-gas configuration will be achieved if the Lewis structure shows eight electrons around each atom. Hydrogen is an exception; its 'Octet' is two electrons, corresponding to two topmost energy level electrons in the noble gas helium.

Examples of the 7 diatomic molecules:

H:H
:N:::N:
O::O

:F:F:
yellow gas



:Cl:Cl:
greenish-
yellow gas


:Br:Br:
red-brown
liquid


:I:I:
dark purplish
solid





3.3 Metallic Bonding

Metals have a tendency of forming cations. Solid crystalline metals can be pictured as a three-dimensional array of positive ions that have fixed positions in the crystal. The valence electrons of these ions move freely throughout the crystal.

http://ithacasciencezone.com/chemzone/lessons/03bonding/mleebonding/metallicbonding.htm

In the solid, the free moving electrons allow for the following properties.

Properties of metallic compounds

Metals conduct electricity and heat.
Metals are malleable, so they can be hammered into different shapes.
Metals are ductile, so they can be drawn into thin wire.
Metals have medium high melting points and most are solids at room temperature.


UNIT 4: CHEMICAL REACTIONS

4.1 Physical and chemical changes

Physical Changes are reversible

There are three states of matter, solid, liquid and gas.

When a substance changes from one of these states to another, this is a physical change.

When a physical change occurs, there is no change of the organisation of how atoms are bonded together; there is a change in the number and strength of forces between the particles in the substance. There is no change in the properties of the substance.

Mixing, grinding, and dissolving are also examples of physical changes.

Physical changes are reversible, examples of methods that can reverse physical change are filtering, evaporation, distillation and chromatography.

When a physical change takes place there may be a change in state or colour but these changes are usually not permanent.

Chemical change creates new properties

When a chemical change occurs there is a change in the organisation of the atoms in the sample. A new substance will be formed with different properties to the original substances.

sodium
+
chlorine
>
sodium chloride
silvery metal
green gas
white crystals



When a chemical change takes place there can be a change in state, colour and a change in energy, which is often observed as heat or light.

Other properties that may undergoe change are malleability, hardness, the ability to conduct heat and electricity and solubility.



4.2 Chemical equations


When a chemical reaction occurs, it can be described by an equation. This shows the chemicals that react (called the reactants) on the left-hand side, and the chemicals that they produce (called the products) on the right-hand side. The chemicals can be represented by their names or by their chemical symbols.

Reactants > Products

Unlike mathematical equations, the two sides are separated by an arrow, which indicates that the reactants form the products and not the other way round.



4.3 Balancing equations

Al + O2 > Al2O3


This is the equation for the burning of aluminum in oxygen. Note that oxygen gas is diatomic. A molecule of aluminum oxide consists of two aluminum atoms combined with three oxygen atoms.

You can see by looking at it that there is something wrong with this equation. A chemical equation must obey the Law of Conservation of Mass, so the total mass of reactants equals the total mass of products. There is only one aluminum atom on the left side whereas there are two on the right. There are two oxygen atoms on the left side, as compared to three on the right side. This clearly doesn't match.




Left side:
Right side:


We can balance the equation by mutiplying the different atoms and molecules on each side by different amounts. Firstly, multiply the aluminum atoms on the left side by 2:


2Al + O2 > Al2O3




Left side:
Right side:


Now there are the same numbers of aluminum atoms on each side of the equation. We could also multiply the number of oxygen molecules on the left side by one and a half (1.5), which would give three oxygen atoms on the left side (1.5 x 2 = 3) to match the three oxygen atoms on the right side:


2 Al + 1.5 O2 > Al2O3







Left side:
Right side:


This is now balanced, but that 1.5 is a horrible thing to have in an equation — how can you have one and a half molecules? We can solve this problem by multiplying everything throughout by 2:


4Al + 3O2 > 2Al2O3








Left side:
Right side:


If you count the number of atoms on each side, you will find that there are four aluminum atoms on each side and six oxygen atoms. Sorted!


4.4 Types of chemical reactions

There are five main types of chemical reactions

1 synthesis
2 decomposition
3 single replacement
4 double replacement
5 combustion

Synthesis, single replacement and combustion reactions all involve the movement of electrons from one element to another element. These reactions can also be described as REDOX reactions.



1 Synthesis reactions

element + element > compound

Sythesis reactions are the basic building blocks in the formation of compounds; a synthesis reaction leads to the formation of a more stable compound. There is often a great deal of energy given out during a synthesis reaction



2 Decomposition reactions

compound > element + element

Decomposition reactions require an external energy source, either in the form of heat or electricity

Decomposition reactions are unusual in the physical world but occur often in nature



3 Single replacement reactions

Single replacement reactions occur when a metal atom is allowed to react with a metal ion

zinc atoms + copper ions > zinc ions + copper atoms
zinc + copper sulphate > zinc sulphate + copper

There is a transfer of electrons from the zinc to the copper.

In a single replacement reaction there is always an element and a compound reacting to make a different element and compound

Reactivity series of metals


The metals can be listed in order from the most reactive to the least reactive. Some of the metals are

sodium most reactive
calcium
magnesium
zinc
iron
tin
copper
silver
gold least reactive


A more reactive metal atom can give its electrons to a less reactive metal ion (the reverse reaction cannot occur)

2Fe + 3Cu2+
>
2Fe3+ + 3Cu

atoms
ions

ions
atoms






4 Double replacement reactions

Double replacement reactions involve two ionic compounds

compound + compound > compound + compound

The cation from the first reactant ends up with the anion of the second and vice versa.

It is impossible for two cations to be together and likewise two anions cannot be together

When a double replacement reaction takes place one of the new compounds formed must be insoluble (i.e. form a precipitate), be water or rearrange itself to form a gas



5 Combustion

All combustion reactions involve oxygen. All the atoms in the other reactant individually combine with oxygen


CH4 + 2O2 > CO2 + 2H2O

Other reactions, which could be considered to be combustion, include corrosion of metals and respiration

Answer 2

Ionic: Valence electrons are lost by the donor to the acceptor atom

Metallic: Valence electrons flow through the entire mass of the metal in an energy level called the conduction band

Covalent: Valence electrons are shared in pairs between the two atoms covalently bonded

Answer 3

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