Elements and the Periodic Table!
The Periodic Table:
Different types of atoms are called elements. Elements are unique and are made of one type of atom. There are 118 known elements. Elements can have different numbers of protons and electrons. this explains all of the differences in the physical properties of matter. Some elements exist at room temperature as gas, some are liquid, and some are solid. All elements are listed and organized in a chart called the Periodic Table. Dmitri Ivanovich Mendeleev was a Russian scientist who invented the periodic table in 1869.
The periodic table is arranged in a grid format. Each element sits in a specific place in the grid, according to its atomic number. The number of protons in an element defines its position in the periodic table, according to the modern periodic law. The atomic number is the number or protons that an atom contains. It's also the number of electrons.
The periodic table contains three major categories of elements...
1. Metals are positioned to the left of the table.
Metals are solid at room temperature (except mercury) which is a liquid at room temperature, are all ductile, meaning they can be pulled into thin wires, lusterous or shiny, they are all good conductors of electricity and heat, malleable or can be hammered into thin sheets, and are prone to lose electrons easily.
2. Metalloids are the ones in the middle.
Metalloids have properties that are a mix of metal and nonmetal properties. They are solid at room temperature, dull or shiny, a mix of good conductors and poor conductors of electricity and heat, and are characterized by having physical properties that tend to be metallic and chemical properties that tend to be nonmetallic.
3. The nonmetals are positioned to the right.
Nonmetals have properties that are opposite from those in metals. They are brittle, dull (not shiny), poor conductors of electricity and heat, solid, liquid, or gasous at room temperatures, and are able to gain or share electrons easily.
Each element on the periodic table is assigned a chemical symbol, which is one or two letters long. The first letter is always uppercase and the second letter (if there is one) is lowercase. For example, H = hydrogen, He = helium, Pb = lead. The letters don't always correspond to the name of the element.
Each square of the periodic table contains the same information about each element...
- atomic number
- chemical symbol
- element name
- average atomic mass
Atomic mass is the average mass of the atom of a specific element.
The periodic table is organized by rows and columns. A horizontal row is called a period and a vertical column is called a group/family. The structure of the table is based on the mass of each element. The elements are arranged from left to right by increasing atomic number. As you go across from left to right, each element has one more electron and one more proton than the element to the left of it. For example, hydrogen, which is the first element in the periodic table and is located at the top left, and has one electron. Helium is next to hydrogen on the right and has two electrons.
A family in the periodic table is a set of elements that share the same properties. The characteristics of each elements display is determined by the number of valence electrons. Valance electrons decide how an atom will react in a chemical reaction. Every element wants to have a full octet, which is typically but not always, eight electrons in the outer shell. To get a full octet, an element will gain or lose valence electrons, the electrons in the outermost shell.
The octet rule says the elements must combine in such a way that each atom has eight electrons in its valence shell, so that it has the same electronic configuration as a noble gas. The five major groups in the periodic table are alkali metals, alkaline earth metals, transition metals, halogens, and noble gases.
In a neutral element, the number of protons equals the number of electrons. This means that the element has a charge of 0. The atomic number tells you the number of protons. If the element is neutral, it also tells you the number of electrons. to find the number of neutrons subtract the atomic number from the mass number.
We use elements every day. For example, aluminum is used to make pots and pans that we cook with, gold is used in jewelry, sodium combined with chlorine is used to make table salt, neon is used to make neon signs, and iron is used to make steel used in bridges or buildings.
Isotopes are atoms of the same element. For example, carbon-14 is an isotope of carbon. Isotopes always have the same number of protons with different atomic masses.
More neutrons = more mass = heavier atoms
Fewer neutrons = less mass = lighter atoms
Each isotope is of an element is identified with a mass number, which is the sum of the atomic number and neutrons in the nucleus.
Mass number = atomic number + number of neutrons
To write an isotope you must know the mass number, atomic number, element symbol, and charge (if it has one).
A positively charged ion or cation results when an atom loses or gives away one or more electrons. A positive ion or cation will be attracted to or a negative ion or an anion. A positive ion will be repelled by another positive ion. A negative ion will be repelled by another negative ion.
The periodic table is governed by periodic law, which states that physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number. Periodic law is considered to be one of the most important concepts in chemistry. It helps chemists to predic how an element will behave. If you know an element's position on the periodic table, you can almost predict its properties.