Periodic Trends!

There are 3 very important trends on the periodic table, that help in understanding why certain elements do the things they do.

The first of these trends is the atomic radius trend.

• To find the atomic radius, you take one half the distance between the nuclei of of two atoms of the same element when they are joined together.
• As the atomic number increases within a group, the charge on the nucleus and the number of energy levels occupied increases. 
• The increase in positive charge draws electrons closer to the nucleus. The increase in the number of occupied orbitals shields electrons in the highest occupied energy level from attraction of protons in the nucleus. The shielding effect is greater than the effect of the increase in nuclear charge, so the atomic size increases.

Next is the ionization energy trend.

• Ionization energy: the energy needed to remove an electron from an atom
• moving electrons from elements on the left side of the periodic table is easy because they only have 1 or 2 electrons in their outer shell
• moving electrons from elements on the right side of the periodic table is harder because they almost have a full shell.

Lastly is the electronegativity trend. It follows the same sequence as the ionization trend.

• Electronegativity: the ability of an atom to attract electrons when the atom is in a compound
• it is low on the left side because they only have 1-2 electrons in the outer shell
• it is high on the right side because they have nearly a full shell. The are more electronegative because they have a stronger pull to fill that last shell.

Collision Theory

The collision theory is what explains how chemical reactions occur. The theory pretty much states that molecules must have enough kinetic energy to react. They must collide in the correct or "appropriate orientation and with sufficient energy to equal or exceed the activation energy.

Activation energy: the minimum amount of energy that particles must have in order to react. "The barrier that reactants must cross to be converted to products.

Activated complex: A "particle" that is an unstable arrangement of atoms that forms momentarily at the peak of the activation energy barrier.

Catalyst (enzyme) : increases the speed of the reaction by lowering the activation energy barrier.

There are two types of chemical reactions, endothermic and exothermic. The graphs for these very well explain the collision theory.

Endothermic reaction: absorbs energy


Exothermic reaction releases energy

Fusion and Fission

Fission: the splitting of a nucleus into smaller pieces, and it is commonly a chain reaction. 

Fission only occurs in two isotopes, Uranium-235 and Plutonium- 239

The only reason the chain reaction occurs is the goal of making that isotope become stable.

Fusion: occurs when nuclei combine to produce a nucleus of a greater mass. 

• Small nuclei combine and release much more energy than fission reactions
• this also only occurs at very high temperatures, like 40 million degrees Celsius!

The chart I have posted below really helped me understand the main differences between the two. 

Comparison chart</> Embed this chart

	Nuclear Fission	Nuclear Fusion
Definition	Fission is the splitting of a large atom into two or more smaller ones.	Fusion is the fusing of two or more lighter atoms into a larger one.
Natural occurrence of the process	Fission reaction does not normally occur in nature.	Fusion occurs in stars, such as the sun.
Byproducts of the reaction	Fission produces many highly radioactive particles.	Few radioactive particles are produced by fusion reaction, but if a fission "trigger" is used, radioactive particles will result from that.
Conditions	Critical mass of the substance and high-speed neutrons are required.	High density, high temperature environment is required.
Energy Requirement	Takes little energy to split two atoms in a fission reaction.	Extremely high energy is required to bring two or more protons close enough that nuclear forces overcome their electrostatic repulsion.
Energy Released	The energy released by fission is a million times greater than that released in chemical reactions, but lower than the energy released by nuclear fusion.	The energy released by fusion is three to four times greater than the energy released by fission.
Nuclear weapon	One class of nuclear weapon is a fission bomb, also known as an atomic bomb or atom bomb.	One class of nuclear weapon is the hydrogen bomb, which uses a fission reaction to "trigger" a fusion reaction.

Types of Radiation

Energy particles that are released released during the decomposition of unstable atomic nuclei are known as radiation. There are three known types of radiation. 

The first type of radiation is Alpha radiation. Alpha radiation is pretty much a stream of positively charged particles which are also known as alpha particles. Alpha particles have an atomic mass of for and a charge of +2, which is actually a helium nucleus. Alpha radiation is the weakest of all radiation, it can be stopped by things like paper and clothing.

The next type of radiation is Beta radiation. Beta radiation is a stream of electrons, which are known as beta particles. Beta radiation can be stopped by things like wood. When a beta particle ejects a neutron in the nucleus turns into a proton which causes the atomic number of the element to increase by one. 

The third type of radiation is Gamma radiation. It is the strongest type of radiation and can only be stopped by a thick wall of lead or concrete. Gamma rays are high-energy photons. Gamma emission does not change the atomic number or the atomic mass. Whenever gamma emission occurs it is usually accompanied by alpha and beta emission as well.

Here is a diagram of the strength of the different types of radiation: