Understanding Atomic Structure

Atomic Structure

• Atoms are the fundamental components of matter participating in chemical reactions.
• Atoms primarily consist of empty space surrounding a compact, dense nucleus.
• The nucleus has protons and neutrons.
• Electrons inhabit orbitals within the empty space around the nucleus.
• The nucleus has a positive charge because of the protons

Subatomic Particles

• Subatomic particles are the constituent parts of an atom: protons, neutrons, and electrons.
• Measuring the masses and charges of subatomic particles uses relative comparisons instead of standard units.
• Relative atomic masses and relative atomic charges describe these comparisons.
• Protons and neutrons possess roughly equal mass, given a relative mass of 1 each.
• Electrons are 1836 times smaller than protons or neutrons, rendering their mass negligible.
• The nucleus is where the mass of an atom is significantly concentrated.
• The positive nucleus attracts negatively charged electrons, holding the atom together.
• When moving at equal velocity in an electric field, the behavior of protons, neutrons, and electrons differ.
• Electrons are easily deflected from a negative plate towards a positive plate.
• This is proof that electrons are negatively charged and have a very small mass.
• Protons deflect away from a positive plate and move towards a negative plate.
• This shows protons are positively charged and heavier than electrons.
• Neutrons do not deflect and has a neutral charge.

Relative Mass and Charge

• Protons have a relative charge of +1 and a relative mass of 1.
• Neutrons have a relative charge of 0 and a relative mass of 1.
• Electrons have a relative charge of -1 and a relative mass of 1/1836.

Determining Subatomic Structure

• The atomic number (Z) indicates the count of protons within an atom's nucleus.
• The atomic number also specifies the number of electrons in a neutral atom.
• The mass number (A) signifies the total of protons and neutrons in an atom's nucleus.
• Neutrons are calculated by subtracting the atomic number from the mass number.
• Protons and neutrons are referred to as nucleons.

Atoms & Ions

• Atoms are neutral, carrying no overall charge.
• Ions form when atoms gain or lose electrons, resulting in a charge.
• The atomic number dictates the element type in both atoms and ions.
• All atoms and ions of the same element share the same number of protons (atomic number).
• The proton number in an unknown element can be found using its mass number and number of neutrons
• Mass number = number of protons + number of neutrons
• Number of protons = mass number – number of neutrons
• Neutral atoms have identical numbers of protons and electrons.
• Ions possess a number of electrons that differs from their atomic number due to their charge.
• A positively charged ion has fewer electrons because it has lost electrons.
• Conversely, a negatively charged ion has more electrons because it has gained electrons.
• The number of neutrons is calculated by subtracting the number of protons from the mass number.

Atomic & Ionic Radius

• Atomic radius measures the size of an atom.
• It is half the distance between the nuclei of two covalently bonded atoms of the same element.
• Atomic radii exhibit trends across the periodic table e.g decreases across each Period
• This is because there is an increase in atomic number and extra electrons are added to the same principal quantum shell
• Atomic radii increase down each Group. Electrons in inner shells shield outer electrons from nuclear charge; weakening the pull.

Ionic Radius

• Ionic radius measures the size of an ion.
• Ionic radii follow trends increase with increasing negative charge, and decrease with increasing positive charge.
• Negatively charged ions form when nuclear charge remains constant, but more electrons are present.
• Outermost electrons become weakly held, increasing the ionic radius.
• Positively charged ions form when atoms lose electrons.
• The nuclear charge remains constant, there is a decrease in the electrostatic force, decreasing the ionic radius.