Analía Bellizzi – Chemistry Classes

Ronald Reagan High School

Atomic Structure

Atomic Structure

An atom is the basic unit of an element. An atom is a form of matter which may not be further broken down using any chemical means

Atoms are composed by many particles, we will concentrate in the main ones: Protons, neutrons and electrons. 

Atoms are composed by SUB-ATOMIC PARTICLES.
An atom contains protons and neutrons  in the nucleus, surrounded by an electron cloud.
If  the atom has a different number of protons, it is NOT the same element!
 

IMPORTANT CONCEPTS

  • The atoms of the same element all have the same number of protons.
  • The atoms of different elements have different numbers of protons
  • PROTONS and NEUTRONS are located in the NUCLEUS
  • These are the only HEAVY particles in the atom. 

HOW MORE MASSIVE?

mass-charge-particles

What you need to know for your exam: 

atomic-particles-2

ATOMIC NUMBER (Z) AND MASS NUMBER (A) – ISOTOPES

ATOMIC NUMBER (Z): The amount of protons in the nucleus gives the element its identity and properties, that’s why it is called atomic number

ATOMIC MASS(A): (ALSO CALLED NUCLEON NUMBER) It’s the total amount of particles in the nucleus. (Protons + Neutrons)

ISOTOPES: Atoms MUST HAVE  the same number of protons if they belong to the same element, but they can also have DIFFERENT amount of neutrons. these different variations of the same element are called isotopes

Atoms with more or less electrons in the electron cloud are called IONS. We have to show the charge when we represent the ion indicating if it is negative, positive and how many charges it has. 

HOW DO WE REPRESENT ATOMS?

The picture shows: X as the element, the zone where we need to indicate the mass and atomic number, so as to the charge of the ion (if any).

atom-representation

Behavior of protons neutrons and electrons in a magnetic field

ELECTRONS are attracted to the positive pole since they have a negative charge

PROTONS are deflected towards the negative pole since they carry a positive charge

NEUTRONS are no deflected since they have no charge so they are no attracted or repelled by the electric field

ELECTRONS are MORE deflected than PROTONS since electrons have a smaller mass. 

deflection of atomic particles