View source for NCEA Level 1 Science/The structure of matter

[[Image:Helium atom QM.svg|thumb|250px|right|An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black).]]

==Introduction==
All '''matter''' is made up of very small particles called '''atoms'''. The name atom comes from the Greek meaning ''uncuttable'', something that cannot be divided further. Atoms are the basic components of '''elements'''.


==Subatomic Particles==
[[Image:Simple_atom_(lithium).png|right|200px]]
Atoms have three subatomic particles:
*'''protons''' (+): positively charged
*'''electrons''' (-): negatively charged
*'''neutrons''' (0): no charge
The can sometimes be written as '''<math>p</math>''' (protons), '''<math>e</math>''' (electrons) and '''<math>n</math>''' (neutrons)

Normally, atoms have no overall charge (are '''neutral''') because ''the number of positively charged protons equals the number of negatively charged electrons''.  The number of neutrons tends to vary and in the case of hydrogen, there are no neutrons. Atoms with the same number of protons but different masses are called '''isotopes'''.

[[Image:Helium_Nucleus.svg|thumb|The nucleus of a helium atom|180px|right]]
Neutrons play a very important role in the functions of an atom. In the nucleus, several protons stay clumped together. As opposite charges attract and like charges repel, normally the protons would repel and scatter the nucleus. However, there is a ''strong nuclear force'' that holds the nucleus together. This incredible force causes nucleons (protons and neutrons) to attract each other with much greater strength than the electric force can repel them, but only over extremely short distances.

[[File:Electron shell 019 Potassium.svg|thumb|left|150px|Potassium has many core electrons; the lone outer electron can easily be lost due to the "shielding" effect.]]

A delicate balance exists between the number of protons and neutrons. Protons, which are attracted to one another via the strong force but simultaneously repelled by their electromagnetic charges, cannot exist in great numbers within the nucleus without the stabilizing action of neutrons, which are attracted via the strong force but are not charged. Oppositely, neutrons lend their inherent instability to the nucleus and too many will destabilize it.

The ''shielding'' (or ''screening'') ''effect'' is similar to effective nuclear charge. The ''core electrons'' repel the valence electrons (electrons on the outer shell) to a certain degree. The more electron shells there are (a new shell for each row in the periodic table), the greater the shielding effect is. Essentially, the core electrons ''shield'' the valence electrons from the positive charge of the nucleus.

[[Image:Stylised atom with three Bohr model orbits and stylised nucleus.png|thumb|200px|width|The red dots are protons and the blue dots are neutrons.]]
===Atomic Number===
The '''atomic number''' is the number of protons in the nucleus of an atom. The atomic number determines what element the atom is. Elements on the '''periodic table''' are listed based on their atomic number. Each individual element has a unique identifying symbol.

If a heavy metal is bombarded with neutrons or a charged particle in an accelerometer and if there is an increase in the number of protons, then atomic number will increase also. This is the method of creating new artificial elements called the ''transuranic elements'' which are elements greater than 92 on the periodic table.

===Mass Number===
The '''mass number''' is the sum of protons plus neutrons in an atom. 

{{Yellow Warning|There is a difference between an atom's mass number and an element's atomic mass.  The mass number measures the number of protons and neutrons in the nucleus of a ''particular atom''.  The atomic mass measures the ''average mass of all atoms for an element''.  For example, a carbon atom might have a mass number of 12 or 14 (or something else), but carbon in general has a mass of 12.011 amu.}}

Magnesium’s atomic mass is 24.3051 but its mass number is 24.


==Electron Arrangements==

An '''element''' is a substance that contains only the same type of atom. That is, the atoms with the same number of protons.


Inside the nucleus, there are protons and neutrons. Electrons orbit the nucleus arranged in different energy levels or '''shells'''. For the first 20 elements, the maximum electron configuration for each shell is:

*1<sup>st</sup> shell: 2

*2<sup>nd</sup> shell: 8

*3<sup>rd</sup> shell: 8

*4<sup>th</sup> shell: 2 (the remaining electrons)

The electron arrangement tells us how many electrons can fit onto each shell.


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; Examples
K (Potassium; atomic number: 19) has an electron configuration of 2,8,8,1.}}


This tells us that there are 2 electrons on the 1<sup>st</sup> shell, 8 on the 2<sup>nd</sup>, 8 on the 3<sup>rd</sup> and 1 on the 4<sup>th</sup>

Another way to calculate the electron configuration for the first 20 elements is by looking at the periodic table. The rows on the periodic table are called ''periods'' while the columns are called ''groups''. 


{{{{BOOKTEMPLATE}}/Periodic Table}}


{{Info|To view a more complete periodic table, take a look at [[/Periodic Table|this periodic table]].}}


To calculate the electron arrangement, we can safely assume for the first 20 elements that the periods in which an element is found is equal to the number of '''shells''' it has. We can also assume that the number of elements in each period up to that shell is the number of electrons in each shell.

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; Examples
Cl (Chlorine; atomic number: 17) is found on '''group''' 7 or 17 and is in '''period''' three. Thus it has 3 shells and 7 electrons on its last shell. Also, its electron configuration is 2,8,7.}}

==Group 1, 2, 16, 17==
===Reactivity===
[[Image:NaCl Formation Lewis.svg|right|200px]]
The ''group'' (column) in which an element is located can determine its reactivity. Elements in group 18 have full valence electrons thus they are ''unreactive'' or ''stable''. These will not form ''compounds'' such as O<sub>2</sub> or CO<sub>2</sub>. On the other hand, group 1 and 17 are ''very'' reactive because they have only one valence electron which is easily lost, thus group 1 and 17 elements are never found alone in nature - they will always be in compounds ie. H<sub>2</sub> and Cl<sub>2</sub>. Group 2 and 16 are ''mildly'' reactive and are also naturally found as compounds.


===Ions===

{{{{BOOKTEMPLATE}}/Table of Ions}}

''Ions'' are atoms or groups of atoms that have gained or lost electrons. The result is that they have become charge particles. 

The ''periodic table'' is divided into two groups: ''metals'' and ''non-metals''. Metals are found on the left while non-metals are found on the right. The elements in the center are metals but they are called ''transition metals''. Metals become positive charged and are called ''cations''. Non-metals become negatively charge and are called ''anions''.  Metals that lose one electrons will have more protons than electrons, so they form positive ions, e.g. H<sup>+</sup> and Al<sup>3+</sup>. Whereas, non-metals that gain electrons will have more electrons than protons, so they form negative ions, eg. Cl<sup>-</sup> and HCO<sub>3</sub><sup>-</sup>.

:*In a chemical reaction, a hydrogen atoms loses its only electron to form an ion of 1 proton and 0 electrons. This Hydrogen ion (H<sup>+</sup>) has a charge of +1 because there is 1 proton while no electrons to balance the charge.

:*A chlorine (2,8,7) atom gains an electron to form an ion of 17 protons and 18 electrons. This chloride ion (Cl<sup>-</sup>) has a charge of -1 because there are 17 protons while there are 18 electrons. The number of electrons is greater than the number of protons by one.

:*Normally, a sodium atom (2,8,1) has 1 electron on its outer shell. In a chemical reaction, it will lose this electron to form a Na<sup>+</sup> ion (2,8).

:*Oxygen (2,6) in a chemical reaction will gain 2 electrons to complete its outer shell. It will form the ion O<sup>2+</sup>.

Atoms desire to have full ''valence'' energy level so it becomes unreactive and ''stable''. This is done by gaining or losing electrons in a chemical reaction. A chemical reaction does not only occur in science labs. Group 1 and 17 are not naturally found in nature. Exposing a group 1 element like sodium to the atmosphere (which contains 78% nitrogen, 21% oxygen, 0.9% argon and 0.03% carbon dioxide) or specifically oxygen would create an immediate oxidisation reaction.

<center>
{| class="wikitable" border="1"
|+ '''Rule of Ions'''
! Lose electrons !! Positive ion
|-
| Gain electrons|| Negative ion
|}
</center>

===Ions and the Periodic Table===
The reactivity and charge of an ions can be linked to its position on the periodic table.

*Group 1 metals have 1 electron on their outer shell therefore they are highly reactive and will lose this electron to form positive +1 ions, eg. Li<sup>+</sup> and Na <sup>+</sup>.

*Group 2 metals have 2 electrons in their outer shell therefore they are mildly reactive and will lose these 2 electrons to form positive +2 ions, eg. Be<sup>2+</sup> and Mg<sup>2+</sup>

*Group 16 non-metals have 6 electrons in their outer shell therefore they are mildly reactive and will gain 2 electrons to form a negative -2 ion, eg. O<sup>2-</sup>, S<sup>2-</sup>

*Group 17 non-metals have 7 electrons on their outer shell. They are highly reactive and will gain 1 electron to form a negative -1 ion, eg. F<sup>-</sup> , Cl<sup>-</sup>

*Group 18 non-metals have full outer  shells. They are unreactive and do not form ions, eg. He, Ne, Ar


<center>
{| class="wikitable" border="1"
|+ '''Charge of Ions'''
! Element !! Electron Arrangement !! Charge
|-
| Hydrogen || <center>1</center> || H +1
|-
| Helium || <center>2</center> || He 0
|-
| Lithium || <center>2,1</center> || Li +1
|-
| Beryllium || <center>2,2</center> || Be +2
|-
| Oxygen || <center>2,6</center> || O -2
|-
| Fluorine || <center>2,7</center> || F -1
|-
| Neon || <center>2,8</center> || Ne O
|}
</center>

===Ionic Compounds===
[[Image:Ionic_bonding_animation.gif|thumb|400px|Sodium and Chlorine ions bonding]]
An ionic compound forms when a positive ion (metals) and a negative ion (non-metals) combine chemically. The process is reactant → product.

There are two types of equations:
*Word equation
*Chemical equation

A word equation involves identifying the reactants and the products. Chemical equations involve using words and symbols to write your equation. In the exam, be sure to read your question properly and write down the type of equation that is asked.

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; Examples
*'''Word equation''': Magnesium + Oxygen → Magnesium oxide
*'''Chemical Equation''': Mg<sup>2+</sup> + O<sup>2-</sup> → MgO}}


==Naming and Writing Formulae==
[[Image:Sodium-chloride-3D-ionic.png|thumb|200px|The crystal structure of sodium chloride, NaCl, a typical ionic compound.  The purple spheres are sodium cations, Na<sup>+</sup>, and the green spheres are chloride anions, Cl<sup>−</sup>.]]

To write ionic compounds, the ''drop and swap'' rule can be utilised.


'''Steps''':

1. Find the ions on the table of ions, then remove the + and – signs

2. If the numbers are the same, they cancel each other out.

3. If the numbers are different, bring them across and drop them.

4. If a number is dropped to a compound, then brackets need to be inserted.


{| class="wikitable" border="1"
|+ '''Examples of the ''Swap and Drop'' rule'''
! Name of compound!! Finding ionic charges !! Numbers swapped and dropped
|-
| Magnesium Oxide || Mg<sup>2+</sup> + O<sup>2-</sup> || MgO
|-
| Aluminium Hydroxide || Al<sup>3+</sup> + OH<sup>-</sup> || (Al(OH))<sub>3</sub> [Unbalanced]
|- 
| Potassium Nitrate || K<sup>+</sup> + NO<sub>3</sub><sup>-</sup> || KNO<sub>3</sub>
|-
| Calcium Chloride || Ca<sup>2+</sup> + Cl<sup>-</sup> || CaCl<sub>2</sub> [Unbalanced]
|-
| Zinc Nitrate || Zn<sup>2+</sup> + NO<sub>3</sub><sup>-</sup> || Zn[(NO<sub>3</sub>)]<sub>2</sub> [Unbalanced]
|-
| Sodium Sulfate || Na<sup>+</sup> + SO<sub>4</sub><sup>2-</sup> || Na<sub>2</sub>SO<sub>4</sub> [Unbalanced]
|}


===Compounds===
[[Image:Copper(II)-sulfate-3D-vdW.png|thumb|150px|Crystal structure of copper sulfate, or CuSO<sub>4</sub>]]
Compounds form when two or more elements combine together eg. CaCl<sub>2</sub>. Subscripted numbers within the formula tell you how many atoms of each element are present.

{{TextBox|1=
; Examples
:* Ca(Cl)<sub>2</sub> - 1 Ca, 2 Cl
:* Mg(OH)<sub>2</sub> - 1 Mg, 2 H, 2 O
}}

Coefficients tell you how many molecules of that compound there are. To calculate the number of atoms of each element present, you multiply the coefficient by the atom number.


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; Examples
:* 3Cu(SO)<sub>4</sub> - 3 Cu, 3 S, 12 O
:* 2CO<sub>2</sub> - 2 C, 4 O
:* 5H<sub>2</sub>SO<sub>4</sub> - 10 H, 5 S and 20 O
:* 3Cu(OH)<sub>2</sub> - 3 Cu, 6 O, 6 H
}}

<noinclude>{{TODO|Add balancing chemical equations section|NCEA Level 1 Science}}</noinclude>
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