Atomic Structure Fundamentals

Atomic Structure

• Face masks help protect from viruses and bacteria but are often not reusable or recyclable.
• Face masks do not kill disease-causing organisms directly.
• Organisms carry negatively charged particles called electrons.
• Face masks can be manufactured with positively charged particles to attract and destroy organisms by destroying their protective coating.
• Masks with positively charged particles can potentially be washed and reused up to 200 times, helping preserve the environment.
• Matter is made up of tiny particles called atoms.
• An atom is the smallest particle that retains the chemical characteristics of an element.
• Different types of atoms contain different numbers of sub-atomic particles, which causes them to behave differently
• The three main types of sub-atomic particles are protons, neutrons, and electrons.
• Protons and neutrons are heavier and grouped in the center of the atom, called the nucleus, and are thus known as nucleons.
• Electrons are lighter and found in electron shells, spaced further from the atom's center.

The Main Sub-atomic Particles

• Protons:
  • Carry a positive electrical charge.
• Neutrons:
  • Are neutral particles with no net electrical charge.
  • Found in the nucleus between protons.
• Electrons:
  • Extremely tiny particles that move very quickly.
  • Carry a negative electrical charge.
• Atoms are electrically neutral because the number of protons equals the number of electrons.

Relative Sizes and Charges of Sub-atomic Particles

• Helium atoms must be magnified millions of times to be seen.
• If protons were the size of footballs, electrons would be the size of full stops about 5km away
• The radius of an atom is approximately 100,000 times larger than its nucleus.
• Neutrons and protons have a relative mass of 1 unit, since they are about the same size.
• Electrons have a relative mass of 1/1840 of that of a proton or neutron
• Protons are located in the nucleus, have a relative mass of 1, and a relative charge of +1.
• Neutrons are located in the nucleus, have a relative mass of 1, and a relative charge of 0.
• Electrons are located in the electron shell, have a relative mass of 1/1840, and a relative charge of -1.

Proton (Atomic) Number and Nucleon (Mass) Number

• The proton number (Z) is the number of protons in its nucleus.
• The proton number is also called the atomic number, because it tells us what element the atom comes from.
• The nucleon number (A) is the total number of protons and neutrons in the nucleus.
  • Nucleon number (A) = proton number (Z) + number of neutrons
• Nucleon number is also called the mass number, because an atom's mass comes mainly from the number of protons and neutrons in its nucleus.
• The mass of electrons in an atom is said to be negligible.
• Number of neutrons = Nucleon number (A) – Proton number (Z)

Nuclide Notation

• Nuclide notation can represent the proton and nucleon numbers of an atom.
• A = nucleon (mass) number
• X = atomic symbol of element
• Z = proton (atomic) number

Sub-atomic Particles in Ions

• An ion is the particle formed when an atom or group of atoms gains or loses electron(s), but the number of protons and neutrons remains the same.
• Ions can indicate how many electrons have been gained or lost through charge numbers.
• Calcium ions, like calcium atoms, have 20 protons and 20 neutrons.
• Calcium ions have a net charge number of +2, indicating there are 2 more protons than electrons.
• A Ca2+ ion has 20 protons and 20 neutrons (just like a calcium atom) but has only 18 electrons.
• An oxide ion has the symbol O2-. This means it has 8 protons and 8 neutrons (just like an oxygen atom), but with a net charge of -2, indicating there are 2 more electrons than protons. It has 8 + 2 = 10 electrons.

Isotopes

• Isotopes are atoms of the same element with the same proton (atomic) number but different nucleon (mass) numbers, resulting in different number of neutrons.
• The number of protons is fixed for all atoms of a given element, while the number of neutrons can vary.
• Neutrons do not affect the electrical charge of the atom, but affect the total mass.
• Isotopes are distributed evenly throughout the nucleus, around and in between the protons.

Electron Shells and Electrons

• Electrons in the innermost shell, closest to the nucleus, have the lowest energy, while those in the outermost shell, furthest away from the nucleus, have the highest energy.
• Each electron shell can only hold a certain number of electrons.
• The first electron shell can hold a maximum of 2 electrons.
• The second and third shells can usually have a maximum of 8 electrons each.
• A helium atom has only 1 electron shell which contains 2 electrons and is thus full.
• Argon has 3 electron shells and 8 electrons in its outermost shell and is in the same group as helium.
• The outermost shell is also called the valence shell, and electrons in that shell are called valence electrons.
• If the valence shell is not full, the atom is reactive and will participate in chemical reactions. Helium and argon atoms have full valence shells of electrons, so they are unreactive.

Explore key concepts of atomic structure. Questions cover the roles of protons, neutrons, and electrons. Understand how these subatomic particles define an element's identity and behavior.