VARIOUS NOTES: THE NATURE OF MATTER and ATOMS

The Nature of Matter

Atoms, Elements & the Periodic Table VOCABULARY WORDS

1.) Matter - anything that has mass and takes up space

2.) Atom - the basic unit of matter that cannot be broken down

3.) Proton - positively charged particles in an atom ( + )

4.) Neutron - uncharged particles in an atom ( 0 )

5.) Electron - negatively charged particles in an atom ( - )

6.) Nucleus - the center of an atom that holds the protons and neutrons

7.) Element - matter made up of one kind of atom

8.) Molecule - a substance that is made up of two or more atoms

9.) Compound - a substance that is made up of atoms of two or more different elements that are chemically combined

10.) Mixture - a combination of 2 or more things that are not chemically combined

11.) Periodic Table - a way to organize all of the elements by their properties and atomic number.

12.) Atomic number - the number of protons in an element

13.) Mass Number - the number of protons and neutrons in an element

14.) Metal - elements that are shiny and are good conductors of heat and electricity.

15.) Nonmetal - elements that are dull in appearance and are poor conductors of heat and electricity.

16.) Metalloid - elements that have characteristics of metals and nonmetals

17.) Group (family)- the columns on the periodic table

18.) Period - rows on the periodic table that have similar properties

19.) valence electrons - the number of electrons on the outside energy level

WE WILL MOST PROBABLY MAKE A PRESENTATION ON THE FOLLOWING TERMS. FAMILIARIZATION OF THESE TERMS WILL HELP YOU GREATLY TO ENSURE SUCCESS ON THE TEST. BEST OF LUCK TO YOU ALL!!

 

I. The Atom

A. The word Atom comes from the Greek work “Atomos” which means “cannot be divided”. The Greek philosopher Democritus (460BC-370BC) came up with the idea that all matter is made up of tiny pieces that cannot be seen.

B. An atom is often defined as the smallest piece of an element that is still considered to be that element. Atoms are the building blocks of all matter.

C. An element is a substance that is made of only 1 type of atom.

D. There are over 90 NATURALLY occurring elements and more than 20 that have been created in a lab. Examples are iron, silver, carbon, gold, oxygen.

E. A Model of the Atom

1. English scientist and teacher named John Dalton(1766-1844) came up with the first model of an atom. He pictured an atom as a hard sphere that was the same throughout. He concluded that:

i. Matter is made of atoms

ii. Atoms cannot be divided into smaller pieces

iii. All the atoms of an element are exactly alike

iv. Different elements are made of different kinds of atoms

v. Different elements combine together to make compounds.

2. Another English scientist, JJ Thomson (1856-1940) discovered that the atom was made of smaller pieces. He is credited with discovering the electron and changing the accepted model of an atom.

. The Electron

a. Used high voltage electricity to discover that part of an atom has a negative charge. He called these negatively charged particles electrons.

2. Thomson’s Atomic Model – a sphere of positive charge with negatively charged electrons spread out evenly among the positive charges. Like a chocolate cookie with electrons scattered throughout.

iii. The negatively charged electrons and the unknown positive charge would then neutralize each other in the atom. Thus the atom is neutral in charge.

3. English scientist Ernest Rutherford (1871-1937) did experiments on atoms that discovered a positively charged center of the atom and that most of the atom was empty space.

i. He shot little particles at gold foil. Most went right through but some bounced off. Ones that went through must mean empty space and the ones that bounced off must mean a positively charged center.

ii. These finding lead to a model of an atom with a nucleus that contains positively charged particles called protons and electrons around the nucleus with space in between.

iii. Rutherford also discovered that particles called Neutrons were also in the nucleus and had no charge.

iv. The new model showed a nucleus made up of protons and neutrons and electrons surrounding it with space in between.

4. Neils Bohr (1885-1962), a Danish scientist made the next change to the model of the atom. Through experiments he determined that the electrons of an atom were located in layers around the nucleus. His model showed levels of electrons around the nucleus with the electrons with the most energy farthest away and lower energy electrons close to nucleus.

5. Current Model – Bohr’s model has been modified to show that the electrons are not located in rigid layers but do arrange themselves by energy levels. This model talks about the electrons moving in waves.

6. The last change to the atomic model has been the discovery that the electrons, protons and neutrons are made up of even smaller parts called quarks, mesons and gluons and others.

3. Parts of the atom

0. Nucleus – the center of the atom that is made up of both the protons and the neutrons. 99.9% of all of the mass of an atom is in nucleus but it contains only .001% of the volume. An atom the size of progressive field would have a nucleus the size of a bumble bee.

2. Proton – Positively charged particle found in the nucleus. All protons are identical, it is the number of protons that determines the identity of the atom. Number of protons is called the atomic number. An atomic mass unit(AMU) is defined as the mass of 1 proton. 600,000,000,000,000,000,000,000 amu = 1 gram!

3. Neutron – A particle with no electric charge that is part of the nucleus. The mass of a neutron is 1amu. The number of protons and neutrons combined is called the Mass Number.

4. Electron – A negatively charged particle that moves around outside of the nucleus. The electron is VERY small – only .0006amu. Electrons move VERY quickly – going around the nucleus billions of times per second! Most atoms have the same number of electrons as protons so they are neutral in charge. The space that the electrons move in is called the ELECTRON CLOUD. Most of this space is empty but this area makes up 99.9% of the total volume of an atom.

2. The Simplest Matter

A. The Elements

1. One Kind of Atom – At least 118 elements are known and about 90 of them occur naturally on Earth. Some synthetic elements have important uses in medical testing and are found in smoke detectors and heart pacemaker batteries.

2. The Periodic Table

1. Charting the Elements – The Periodic Table of Elements helps to organize and display elements. Each element is represented by a chemical symbol that contains one to three letters. The elements are organized by their characteristics (properties) into rows and columns. The rows are called periods. Elements in a row have the same number of energy levels. Columns are called groups. Elements in each group have similar properties related to their structure. They tend to have similar bonds.

3. Identifying Characteristics – Each element is different and has unique properties. These differences can be described in part by looking at the relationships between the atomic particles in each element.

1. Atomic Number – The atomic number tells us the number of protons in an element. No two elements have the same atomic #.
2. Atomic Mass – The atomic mass is the weighted average mass of the isotopes of an element (i.e. protons + neutrons). The atomic mass unit is given the symbol u.

3. Compounds and Mixtures

A. Substances – Matter that has the same composition and properties throughout is called a substance.

1. Compounds – A compound is a substance whose smallest unit is made up of atoms of more than one element bonded together. Compounds often have properties that are different from the elements that make them up.

a. Compounds Have Formulas- H2O tells you which elements make up a compound as well as how many atoms of each are present. The subscript number tells you how many atoms of that element exist in one unit of that compound. No subscript is used when only one atom of an element is present. A given compound always is made of the same elements in the same proportion.

2. Mixtures – When two or more substances (elements or compounds) come together but don’t combine to make a new substance, a mixture results. The proportions of the substances in a mixture can be changed without changing the identity of the mixture. Air is a mixture. Air is a mixture of nitrogen, oxygen, and other gases, which vary at different times and places.

a. Separating Mixtures – Sometimes you can use a liquid to separate a mixture of solids. Sugar and sand, only the sugar dissolves in the water. The sand then can be separated from the sugar and water solution by pouring the mixture through a filter. Heating the remaining solution will separate the water from the sugar. Separating a mixture of solids of different sizes might be as easy as pouring them through successively smaller sieves of filters.

b. Homogeneous or Heterogeneous – Mixtures can be classified as homogenous or heterogeneous. Homogeneous means “the same throughout”. A heterogeneous mixture has larger parts that are different from each other.

Familiar Element Name & Symbols…(NOT ON TEST UNLESS SPECIFICALLY STATED BEFOREHAND)

Hydrogen H

Uranium U

Helium He

Plutonium Pu

Lithium Li

Magnesium Mg

Beryllium Be

Aluminum Al

Boron B

Silicon Si

Fluorine F

Phosphorus P

Neon Ne

Sulfur S

Carbon C

Argon Ar

Nitrogen N

Oxygen O

Chlorine Cl

Sulfur S

Sodium Na

Iron Fe

Potassium K

Copper Cu

Silver Ag

Gold Au

Lead Pb