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Atomic structure
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Atomic Structure
Atoms can be thought of as the building blocks of all matter. Everything in the whole universe is made up of trillions of atoms.
Overview:Ā
What are the parts of an atom?Ā Ā Ā Ā Ā Ā Ā
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Ā Ā Ā Ā Ā Ā Ā Ā Atoms are made of three types of subatomic particles which are labeled on the right
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Protons: protons are positively charged particles found in the nucleus (center) of the atom. They are shown with a "+" to indicate their charge.
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Neutrons: neutrons are found in the nucleus along with protons. These particles are neutral meaning they do not carry any charge.
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Electrons: electrons are negatively charged particles which orbit the nucleus in shells/energy levels. They are shown with a "-" to indicate their charge.
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Pearson Scott Foresman, via Wikimedia Commons. Public Domain.
The Nucleus:Ā
The nucleus:Ā
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The nucleus is the center of the atom which houses protons and neutrons. The outer shells of electrons orbit the atom's nucleus as shown above. Compared to the rest of the atom, the nucleus is very small, but carries most of the atoms mass from protons and neutrons. Due to the positively charged protons, the nucleus has a positive charge. This charge pulls in the outer shells which cause them to orbit.
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Protons:Ā Ā Ā Ā Ā Ā Ā
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Atomic number is how many protons are in the nucleus. The fourth element, Beryllium (shown above) has four protons in its nucleus. Therefore, the atomic number of Beryllium is four.
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Protons along with neutrons determine the atom's mass. The mass of an atom is measured in atomic mass units or amu. One proton and one neutron are approximately 1 amu each. Adding the protons and neutrons in an atom will give you the atomic mass.
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Neutrons:Ā Ā Ā Ā Ā Ā Ā
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Neutrons are neutral and carry no charge. Unlike electrons, neutrons are not always equal to the number of protons. One neutron is one amu.
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Q - What is the atomic mass of an atom with 9 protons and 10 neutrons?
Electron shells
Electrons orbit the nucleus in shells/orbitals/energy levels. The number of electrons is always equal to the number of protons to maintain a neutral charge in the atom.
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These shells each contain a specific number of electrons and are filled in a certain order. Each shell can occupy up to a certain number of electrons. They are named as K, L, M and N. Basic chemistry uses the following:
1st Shell - 2 electrons
K
2nd Shell - 8 electrons
L
3rd Shell - 8 electrons
M
4th Shell - 18 electrons
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Electrons fill the first energy level, then second and so on. The electrons in the outermost shell of the atom are called valence electrons, which are the only electrons that are involved in bonding or chemical reactions.
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During bonding or chemical reactions, atoms will either lose or gain valence electrons to become more stable.ā
The four electrons of a Beryllium atom will fill two of the shells. The maximum occupancyĀ
of the first shell (K) is two electrons. The remaining two will orbit in the second shell (L).
These two are the valence electrons which take part in chemical bonding/reactions.
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Practice:Ā 1. Draw the shells of a Nitrogen atom with 7 electrons
Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā 2. Draw the shells of an Aluminum atom with 13 electrons
Pearson Scott Foresman, via Wikimedia Commons. Public Domain.
Ions:Ā
All atoms want to have a full complete shell, without valence electrons. They achieve this by either losing or gaining electrons in their valence shell. After losing/gaining, they are called ions.
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Cations:Ā
Some atoms will lose their valence electrons so that they are stable. Atoms can lose up to four electrons. However, doing this will affect the charge. Why? Atoms by themselves are neutral, due to the balance of protons and electrons. When atoms lose electrons, they acquire a positive charge, as there are now more protons than electrons in the atom. Positively charged ions are called cations.
Magnesium is a metal with an atomic number of 12. There are two valence electrons, which will be lost giving Magnesium a charge of +2.
Q: What will the charge of an element with an atomic number of 19 be?
Anions:Ā
Other atoms will gain electrons to complete their valence (outermost) shell.Ā Doing this results in a negative charge, because there are now more electrons than protons in the atom. Negatively charged ions are called anions.
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Nitrogen is a gas with an atomic number of 7. There are five valence electrons, however it can only lose up to four. Instead, nitrogen will gain 3 electrons giving it a charge of -3.
Q: What will the charge of an element with an atomic number of 9 be?
How to Answer Questions: (Read if stuck)ā
1. First, draw the atom with the Bohr model (as shown with Beryllium atom above)
2. Distribute electrons throughout the shells according to their occupancy
3. Find the valence electrons which are in the outermost shell
4. Decide if the atom will gain or lose electrons
5. Determine what the charge will be after gaining/losing
Ex.
If losing 2, the charge will be +2, if gaining 2 the charge will be -2. (Pay attention to charges!)
Summary:Ā
Nucleus - center of atom
Protons - positively charged particles in the nucleusĀ
Neutrons - neutral particles in the nucleus
Ion - an atom that has lost or gained electrons
Cation - positively charged ion (result of losing electrons)
Anion - negatively charged ion (result of gaining electron)
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