Atoms, Elements, & Periodic Table
Physical Change:
This week we will be discussing physical and chemical changes. In a physical change, an object undergoes a change that does not change its chemical matter. For example, if you cut an apple into 4 pieces, you still have an apple it's just in smaller pieces. Another example is water changing from ice to a puddle. It's still water! Even if you boil it, it's still water. State of matter changes are physical changes.
Properties of a physical change include change in: texture, shape, size, color, odor, volume, mass, weight, and density.
Chemical Change:
In a chemical change bonds are broken and new bonds are formed between different atoms. Whenever chemical reactions occur, the atoms are rearranged and the end product is a completely new substance. For example, if you leave your cut apple out, the oxygen in the air mixes with the apple's enzymes and causes it to turn brown. You can not change it back to its original state. Thus, a chemical change has occurred. Another example is burning a log. When you burn the log ash is produced. You can not take this ash and turn it back into a log. You have created something new. A chemical change has occurred.
Properties of a chemical change include: change in color, bubbling/fizzing, light production, smoke, and the presence of heat.
Here are some examples of chemical changes
Structures of Matter
An atom is a small particle that makes up most types of matter. The law of conservation of matter states that matter is not created or destroyed – it only changes from one form to another.
Democritus is credited with introducing the idea of the atom. He believed that different types of matter had their own unique atoms.
John Dalton’s experiments led to the atomic theory of matter.
J.J. Thomas discovered the electron using anodes (positive charges) and cathodes (negative charges). Through his experiments he discovered electrons, which are negatively charged particles. Matter that has an equal positive and negative charge is said to be neutral.
Ernest Rutherford concluded that the atom is mostly empty space, he named the positively charged central part of the atom the nucleus, the positively charged particles in the nucleus are called protons, and suggested that electrons were scattered in the empty space around the nucleus.
James Chadwick discovered that sometimes atoms give off new particles. These new particles have no charge and are therefore named neutrons.
Niels Bohr suggested that electrons move in energy levels. The lowest energy level is closest to the nucleus and the highest is farther away from it. Electrons move in planet like orbits around the nucleus in a space that is known as the electron cloud.
Physicists today have been able to break down protons and neutrons even further into what are called quarks.
What is an element?
An element is matter made up of only one kind of atom. At least 115 elements are known and 90 of those occur naturally on Earth. Elements make up gases, minerals, and liquids. Natural elements are things like oxygen, gold, and aluminum. Elements that are not naturally occurring are known as synthetic elements. These elements are made by scientists and are used for things like medical testing, smoke detectors, and pacemaker batteries. To organize and display all of these elements, chemists have created a chart called the Periodic Table of Elements. Each element is represented by a chemical symbol that contains one to three letters. All the elements in the same row have the same energy level. The elements in each group have similar properties related to their structure. They also form similar bonds.
The atomic number of an element, tells you the number of protons in the nucleus of an atom and the number of electrons orbiting around the atom. We know that subtracting the atomic number from the atomic mass gives us the amount of neutrons in an atom.
The proton and neutrons are in the nucleus of an atom. The electrons circle around the nucleus in what's known as the electron cloud.
What when I take an element and change its atomic mass?
The neutrons would change. This is how we get isotopes. ‘Iso’ means same. Isotopes are atoms with the same atomic number, but different atomic mass, therefore they have a different number of neutrons. (Think of twins. They look alike but they are different).
Metals
Elements fall into three general categories: metals, nonmetals, and metalloids. Metals usually have a shiny luster and are good conductors of electricity. ***All metals except mercury (Hg) are solid at room temperature. It is a liquid **** Metals are malleable which means they can be bent.
Nonmetals
are usually dull in appearance. Most are poor conductors of electricity. Many are gases at room temperature but some are liquids while others are gases. ***Nonmetals make up about 97% of our bodies.***
Metalloids
are elements that have characteristics of metals and nonmetals. (transition metals). All metalloids are solid at room temperature. They are shiny and conduct electricity but not as good as metals.
Compounds and Mixtures
A substance is matter that has the same composition and properties throughout. A compound is a substance produce when elements combine. This substance is different from any of the single elements. Ex: Water, Hydrogen peroxide
When two or more substances, elements, or compounds come together but don’t combine to make a new substance it is called a mixture. Mixtures can be separated back into their original parts. Ex: Sand & water, salt water, salad
Homogeneous=the same Hetero = different A homogeneous mixture is a mixture that is the same throughout. where you can’t see the different parts. Heterogeneous mixtures are not the same. They have larger parts that are different from each other.
How To Read The Periodic Table
The periodic table is arranged according to the number of protons that each element has. Helium which has 1 proton all the way up to Ununoctium which has 118 protons. When you look at the horizontal rows of the Periodic Table, the elements are arranged from left to right in PERIODS. Each element of the same period will have a similar electron configuration. When you look at the vertical columns of the periodic table, the elements are arranged in GROUPS and the elements in each group have similar characteristics and will react similarly in certain situations. As you move down each column the element's reaction will get stronger. For example, group one, the Alkali Metals react with water. Hydrogen will have the weakest reaction while Francium will have the strongest. The video below shows a reaction with Lithium, Sodium, and Potassium in water.
