Each element has a unique name and is represented by a unique symbol
- Chemical symbol: a one- or two-letter designation for an element derived from the element’s name
- First letter of the symbol is always capitalized
Father of the Periodic Table
Mendeleev
Periodic Law of the Elements
when elements are arranged in a particular order (increasing atomic number), elements of similar properties occur at periodic intervals
Elements are arranged into
- Groups/families – vertical columns
* Periods – horizontal rows
Metals
Have luster, are malleable, conduct electricity
Nonmetals
Do not have the properties of metals
Metalloids
Have some metallic properties and some nonmetallic properties
Atom
- The smallest individual particle of an element that maintains the properties of that element
- Atomos - indivisible
Dalton’s Law of Atomic Theory
- All matter is composed of extremely small particles called atoms.
- Atoms of a given element are identical in their physical and chemical properties.
- Atoms of different elements differ in their physical and chemical properties.
- Atoms of different elements combine in simple, whole-number ratios to form compounds.
- In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed.
An atom is the smallest particle of an element that can exist and still have the properties of the element, known also as
. The fundamental building block of matter.
Today, we know that atoms are made up of smaller, more fundamental particles called
subatomic particles
Protons, Electrons & Neutrons
An atom consists
- Of a nucleus that contains protons and neutrons
* Of electrons in a large empty space around the nucleus
An atom is composed of a nucleus and an area called the electron cloud
- The nucleus is very small compared to the size of the atom
- The nucleus contains the protons and the neutrons
- The electrons are constantly moving around in the electron cloud
- In a neutral atom, the number of electrons is equal to the number of protons
The atomic number
Is specific for each element
Is the same for all atoms of an element
Is equal to the number of protons in an atom
Appears above the symbol of an element
Ions
- Charged particles that have either lost or gained electrons
- These have the same number of protons and neutrons, but a number of electrons that differs from the number of protons
Isotopes
Atoms of the same element (same number of protons) with different numbers of neutrons
The mass of atoms is measured in units of
atomic mass unit
Masses reported on the periodic table are
weighted averages
The atomic mass of an element
- Is listed below the symbol of each element on the periodic table
- Gives the mass of an “average” atom of each element compared to 12C
- Is not the same as the mass number
Mass Number
the number of protons plus the number of neutrons
Atomic Weight/Mass
the mass of an average atom
The calculation for atomic mass requires the:
- Percent (%) abundance of each isotope
- Atomic mass of each isotope of that element
- Sum of the weighted averages
