Periodic Trends

Introduction to ions Atoms are electrically neutral because they have equal numbers of protons and electrons When an electron is either gained or lost by an atom, it is no longer electrically neutral and it becomes an ION or a charged atom. Example: Lithium 3 Protons +3 3 Electrons -3 Overall Charge: 0 - neutral

Positively charged ions: CATIONS Loss of an electron causes the sodium atom to have more positive charge in the nucleus than negative charge. Losing one electron gives it a 1+ charge.

Negatively charged ions: ANIONS Gain of an electron gives chlorine more negative charge than positive, so it becomes a 1- ion.

Ionization Energy To remove an electron from an atom to make it a cation involves energy. This is called Ionization Energy and it is measured in kJ/mol.

Ionization Energy The energy needed to remove an electron from an atom or ion in the gaseous state. The higher the ionization energy, the harder it is to remove the electron.

Ionization Energy Ionization energy for Fr (87)_____________________ kJ/mol Ionization energy for F(9) ______________________kJ/mol From which atom is it easier to remove an electron?_________ From which atom is it harder to remove an electron?_________

Periodic Trends Ionization Energy – Down a group As you move down a group, the size of the atom increases because it adds more and more orbitals. The further away the electrons are from the nucleus and its attractive forces, the easier it is to remove. Lithium Sodium Potassium Rubidium

Periodic Trends Ionization Energy – Down a group Electron Shielding also plays a role as you move down a group. The inner electrons shield the outermost electrons from the attractive pull of the nucleus. This causes the electrons to be held less tightly by the nucleus. This means it will be easy to remove them from the atom.

Periodic Trends Ionization Energy – Across a Period One electron and one proton is added to the atom If the electron is added to the same energy level, the higher nuclear charge (from the additional proton in the nucleus) attracts the outer electrons more strongly. Thus the energy required to remove and electron becomes larger. Li Be B C N O F

Periodic Trends Ionization Energy Graph – Across a Period Example: Li has 3 electrons and 3 protons. Neon has 10 electrons and 10 protons. This large number of protons holds the electrons more tightly than Li’s 3 protons can.

Periodic Trends Atomic Radius It’s hard to measure the size of one atom alone. One method to measure an atom is to calculate the bond radius, which is the length that is half the distance between nuclei of two bonded atoms.

Periodic Trends Down a group Increases as you move down a period due to increase in the number of orbitals As a result of this, electrons are not pulled close to the nucleus and are easily pulled off

Atomic Radius Across a period Decreases because the added protons pull the electrons closer, making the atom physically smaller

Graph of Atomic Radius

Periodic Trends Electronegativity A measure of the ability of an atom to attract electrons. The larger the electronegativity, the more the atom attracts electrons.

Electronegativity Across a period Increases because more protons are added to the nucleus, which allows it to attract negatively charged electrons.

Electronegativity Down a group: Decreases because the larger size of the atom decreases the pull from the nucleus so electrons are not attracted to it.

Electronegativity Graph

Ionic Radii When metal atoms lose electrons, they lose an entire energy level. This makes the atom’s radius smaller. Normal size Decreased ionic size

Ionic Radii When atoms gain an electron, it makes them larger because the electrons repulse (push away from) each other. Normal size Increased ionic size