Science 8th grade notes

DAY 1

MEMORIZE:

Water is H₂O
Carbon dioxide is CO₂
Glucose is C₆H₁₂O₆
Table salt is NaCl
Oxygen is O₂
Household bleach is NaClO
Hydrochloric acid is HCl
Ammonia is NH₃
Baking soda is NaHCO₃
General vinegar is HC₂H₃O₂
Organic vinegar is CH₃COOH

[END MEMORIZATION OF BULLET POINTS]

Matter is anything that takes up space and has mass

it's anything you can touch taste or smell

Weight is mass times G forces (acceleration due to gravity)
All matter is made up of atoms these tiny things make up big things
Ancient Greeks had a philosophical idea that all nature must be made up of some very small thing that can not be divided
The word atom comes from a Greek word meaning cannot be divided

Atoms are the basic building blocks of all matter

Atoms are made up of 3 smaller parts these are called the subatomic particles. The three subatomic particles are:

The Proton (Positive charge)
The Neutron (Neutral charge)
The Electron

The proton and the neutron make up the center nucleus of the atom *(not to be confused with the nucleus of a cell)

The number of protons determines what type of atom it is
The proton and neutrons are the majority of the mass of an atom

A type of atom is called an element

If an atom has six protons it is the element called carbon
The number of protons is called the atomic number
The atomic number is the definition of each type of element

The neutrons are important but do not determine the identity of the element

Just as you are you, and your clothes or haircut, while important are not what defines you

DAY 2

In an ideal atom the number of protons equals the number of neutrons and the number of electrons

The electron can be abbreviated e-
The nucleus is surrounded by a cloud of e-

The structure of an atom is a nucleus of protons and neutrons surrounded by a cloud of e-

If the nucleus of an atom was the size of a poppy seed the electron cloud would be the size of Carter Finley Stadium

Many experiments were done to help reach this understanding

Earnest Rutherford (1871-1937) performed one of these experiments
Rutherford shot a beam of radioactive helium at a very thin piece of au foil
He expected they would most likely go through with the few getting bit a little by the charges of the e- that had been recently discovered and most of the particles did exactly that
But there were some that bounced straight back this was very surprising
“It was as if you fired a 15 inch shell at a piece of tissue paper and it came back and hit you”

Periodic table

We needed a way to organize all these different atoms so we could keep track of them
Dimitri Ivanovich Mendeleev was a Russian chemist who had an idea about how to organize all these different types of atoms
He started to notice that certain elements had things in common
He felt that the elements could be organized based on atomic mass
He put them in a chart based on these groupings

DAY 3

We still use the basic model of the periodic table that Mendeleev first developed in 1871. It has been updated with more discoveries and new elements.

DAY 4

Periodic table

Each element on the periodic table will have lots of information around it
The most prominent in the box is the one or two letter symbol
Another is the element name
The name will be in Latin Greek German or English
New elements are often named for where it was found or to honor a famous scientist
Another is the atomic number
This is the number of protons in its nucleus
This is a whole number that is unique to the element
If you change the atomic number you change the element

While Mendeleeve first proposed sorting the periodic table by atomic mass we now arrange the elements by atomic number

The last thing in the box is the atomic mass

This is the mass of the atom as it is usually found in nature
Some atoms of the element that are in the world around us will have more or less neutrons than protons

DAY 5

Periodic table

How to calculate the usual number of neutrons

Atomic mass number rounded to a whole - atomic number = number of neutrons most often found in a naturally occurring sample

For example the number of neutrons in Boron would be 6 because the atomic mass is 10.811 which would round to 11 and the atomic number is 5 so 11 - 5 = 6

Electrons can be said to be in layers around the nucleus

These are spherical layers kind of like nesting dolls
The closer to the center the smaller the doll
The layers of electrons called energy levels are also smaller when closer to the nucleus
Smaller atoms will have less atomic mass and fewer levels
There is a relationship between the row on the periodic table and the number of energy levels

The rows across the periodic table are called periods

The top row is called period one
Period one has 1 energy level
The electrons in each level also follow a pattern
The electrons must fill a row from left to right before starting on the next period

DAY 6

The Columns of the periodic table are called groups

Elements in a group will have the same number of outer shell electrons
The electrons fill the energy levels from left to right
Within a group all the elements will have the same number of electrons in its outer energy level or shell
If elements have the same number of outer shell electrons then they will react in a similar fashion

Ex: K and na are in the same group and react in similar ways because they have the same number of outer shell electrons

The outermost energy level electrons are called valence electrons

CA and K are in the same period but do not react in a similar way
Niels Bohr (1885 - 1962) was a Danish physicist who developed a way to draw how electrons can be found around atoms
He wanted a way to visualize the energy levels

How to draw the Bohr model of the first 20 elements

Make a solid dot to represent the nucleus
Determine the number of electrons an electrically neutral atom

Electrons equal atomic number

Follow this pattern:

First energy level can hold two electrons
Second and third row can hold eight electrons

Fill from the inside out in this pattern