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Rachel Wong

on 24 October 2014

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Transcript of Atom

Everything around us is made up of atoms
What is an atom?
The Structure of the Atom
- The nucleus is made up of protons and neutrons
- Protons have a positive electrical charge (+)
- Neutrons have a neutral charge
The Nucleus
- There are two subatomic particles that determines the mass of an atom
- The electrons mass is not included because the mass is very little compared to the protons and neutrons
- The mass relative of a proton to an electron is 1840a.m.u to 1a.m.u.
- The electrical charge particles in the atom have no overall electrical charge as the opposite charges will balance each other out
The Electrons
- The electrons orbit the nucleus creating what's called an electron cloud.
- They have a negative electrical charge (-)
- The electrons that surround the nucleus have fixed energy levels called electron shells.
Electronic Configuration
- Within each shell (K.L.M.N respectively) there are different energy levels called sub shells s,p,d and f.
- Each shell can only contain a certain number of electrons.
- The electrons in the outermost shell, valence shell, determines the chemical properties of the atom.
The Mass of an Atom
- As electrons gain or lose energy, they jump between energy levels.
- The outermost shell has the highest energy level.
All atoms found are arranged in what's called a Periodic Table
The periodic table is arranged in a specific order by their atomic number
The elements are arranged in:
Group determines the number of electrons in the outer (valence) shell
Period determines the number of electron shells of an element
The periodic table is divided into three main sections: metals, metalloids and non-metals.
- The metalloids separates the metals and the non-metals.
- Metalloids have both metallic and non-metallic properties.
- The atomic number determines the number of protons and electrons in the atom
- The atomic mass determines the number of protons and neutrons in the atom
- The different number of protons in an element determines the type of atom
- The number of electrons determine the chemical properties of an element
- Most mass of the atom is concentrated in the nucleus
Trends in the periodic table
Periodic trends are patterns that exist within the periodic table that demonstrate certain properties of an element. The trend increases or decreases when going down a group or across a period (left to right).

A few trends in the periodic table are:
- Atomic radius
- Electronegativity
- Metallic nature
- The atomic radius decreases going across a period, while increases going down a group
- As the number of protons increases across the period the radius of the atom decreases because the electrostatic attraction between the electrons and the nucleus pulls the outermost electrons closer to the nucleus.
- The atomic radius increases going down a group because the electrons are added to successive main shells.
- The electronegativity of an element increases going across a period as the number of outer (valence) shell increases and the force of attraction towards electrons grow stronger.
- As elements become more metallic, the electronegativity increases.
- The electronegativity going down a group decreases as the elements become more metallic and they are more likely to lose electrons rather than attract electrons.
- In this case, Fluorine has the most electronegativity and Francium has the least electronegativity.
- The metallic nature of the elements decreases going across a period, while it increases going down a group.
Thank you for watching!
By Rachel Wong
Full transcript