Atomic Structure and Periodicicity Chapter 7 Atomic Structure and Periodicicity

Terms Atomic Number Groups Periods Quantum Numbers Aufbau Principle Pauli Exclusion Principle Hund’s Rule Atomic Radius Ionization Energy Electronegativity

Atomic Number, Z The atomic number of an element is the number of protons in the nucleus of an atom of that element. Atoms of an element that are chemically alike but differ in mass are called isotopes of the element. Atoms of the same element (Z) but different mass number (A).

Number of neutrons = mass number – atomic number The mass of a neutron is almost the same as the mass of a proton. The sum of the protons and neutrons in the nucleus is the mass number of that particular atom. Number of neutrons = mass number – atomic number

ATOMIC STRUCTURE Particle Charge Mass proton + charge 1 neutron No charge 1 electron - charge Too small

n describes the electron energy shell. The Principal Quantum Number - n n describes the electron energy shell.

The farther an electron is from the nucleus, the greater the numeric The Principal Quantum Number - n The farther an electron is from the nucleus, the greater the numeric value for n.

For the known elements, n = 1 through 7 The Principal Quantum Number - n For the known elements, n = 1 through 7

n = 1 through 7

The maximum number of electrons in n is 2n2 The Principal Quantum Number - n The maximum number of electrons in n is 2n2

Energy level 1 can have a maximum of ____ electrons. The maximum number of electrons in n is 2n2 Energy level 1 can have a maximum of ____ electrons.

2 The maximum number of electrons in n is 2n2 Energy level 1 can have a maximum of ____ electrons. 2

The maximum number of electrons in n is 2n2 Energy level 2 can have a maximum of ____ electrons.

8 The maximum number of electrons in n is 2n2 Energy level 2 can have a maximum of ____ electrons. 8

The maximum number of electrons in n is 2n2 Energy level 3 can have a maximum of ____ electrons.

18 The maximum number of electrons in n is 2n2 Energy level 3 can have a maximum of ____ electrons. 18

The maximum number of electrons in n is 2n2 Energy level 4 can have a maximum of ____ electrons.

32 The maximum number of electrons in n is 2n2 Energy level 4 can have a maximum of ____ electrons. 32

The Angular Quantum Number - l l describes the electron energy subshell or shape.

The Angular Quantum Number - l Each electron energy level n, has n-1 sublevels.

Energy level 1 has ____ sublevels. Each electron energy level n, has n sublevels. Energy level 1 has ____ sublevels.

Energy level 1 has ____ sublevels. Each electron energy level n, has n sublevels. Energy level 1 has ____ sublevels.

Energy level 2 has ____ sublevels. Each electron energy level n, has n sublevels. Energy level 2 has ____ sublevels.

Energy level 2 has ____ sublevels. 1 Each electron energy level n, has n sublevels. Energy level 2 has ____ sublevels. 1

Energy level 3 has ____ sublevels. Each electron energy level n, has n sublevels. Energy level 3 has ____ sublevels.

Energy level 3 has ____ sublevels. 2 Each electron energy level n, has n sublevels. Energy level 3 has ____ sublevels. 2

Energy level 4 has ____ sublevels. Each electron energy level n, has n sublevels. Energy level 4 has ____ sublevels.

Energy level 4 has ____ sublevels. 3 Each electron energy level n, has n sublevels. Energy level 4 has ____ sublevels. 3

The Angular Quantum Number - l Sublevels in the known elements are represented by the letters s, p, d, and f.

s p d f

The Magnetic Quantum Number - m m describes the orbital within the sublevel or orientation.

The Magnetic Quantum Number - m s sublevel = 1 orbital p sublevel = 3 orbitals d sublevel = 5 orbitals f sublevel = 7 orbitals

The Magnetic Quantum Number - m Each orbital can hold a maximum of 2 electrons.

Pairs of squares on the periodic table are orbitals.

The s-block has 1 orbital.

The p-block has 3 orbitals.

The d-block has 5 orbitals.

The f-block has 7 orbitals.

The Spin Quantum Number - s s describes the spin of the electron.

The Spin Quantum Number - s Electrons in the same orbital must have opposite spins.

The Spin Quantum Number - s Possible spins are clockwise, + 1/2, and counterclockwise, - 1/2.

Shape of 1s Orbital

Shape of 2p Orbital

Shape of 3d Orbitals

Quantum Numbers and Atomic Orbitals An atomic orbital is specified by three quantum numbers. n the principal quantum number - a positive integer l the angular momentum quantum number - an integer from 0 to n-1 ml the magnetic quantum number - an integer from -l to +l The three quantum numbers are actually giving the energy of the electron in the orbital and a fourth q.n. is needed to describe a property of electrons called spin. The spin can be … The spin q.n., ms can be + ½ or - ½ .

Written Notes for sections 7.1-7.5 Use Handout Stop Written Notes for sections 7.1-7.5 Use Handout

Electron Configuration Three rules apply The aufbau principle/rule The Pauli exclusion principle/rule Hund’s rule These all define how an electron is arranged.

Aufbau Principle States: each electron occupies the lowest energy orbital available. So, the first step in determining the ground-state is learning the sequence of atomic orbital's from lowest to highest energy levels. The aufbau Diagram

The aufbau Diagram

The aufbau Diagram: Features In order of increasing energy, the sequence of energy sublevels within a principal energy level is s, p, d, and f.

Noble Gas Notation If the element is past the first noble gas of the Periodic Table you can use noble gas notation to write the electron configuration. Sodium is past both He and Ne therefore we can write its electron configuration like… [Ne] 3s1 This is saying you go to Neon then to the 1 element on the 3rd row.

Electron Configurations… …are the way electrons are arranged in various orbitals around the nuclei of atoms. Three rules tell us how: Aufbau principle - electrons enter the lowest energy first. This causes difficulties because of the overlap of orbitals of different energies – follow the diagram! Pauli Exclusion Principle - at most 2 electrons per orbital - different spins

Electron Configurations Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to. Let’s write the electron configuration diagram for Phosphorus We need to account for all 15 electrons in phosphorus

Orbitals fill in an order Lowest energy to higher energy. Adding electrons can change the energy of the orbital. Full orbitals are the absolute best situation.

Atomic Radius Move down a group: Increases Move Left to Right: Decreases

Atomic Radii for Selected Atoms

Group trends: Atomic Radius H Li Na Mg Al Si P S Cl Ar K Rb 57

Ionization Energy To form an ion you need ENERGY! The energy needed to overcome the attraction between the positive energy in nucleus and the charge of the electron. This is the IONIZATION ENERGY I.E. can be thought of as an indication of how strongly an atom’s nucleus holds onto the valance electrons.

Ionization Energy A high I.E. means the atom has a strong hold on its valance electrons. A low I.E. means the atom loses its valance electrons easily. It is possible for atoms to lose of gain more than one electron. The amount of energy required to do this is called the second ionization energy. So the third is…

Ionization Energy First ionization energy: increases from left to right across a period; decreases going down a group.

Trends in Ionization Energies for the Representative Elements

Electronegativity Electronegativity indicates the relative ability of its atom to attract electrons. As you move from left to right in a period the electronegativity increases. As you move down in a group the electronegativity decreases. The lower left side of the periodic table has the lowest and the upper right has the highest!!

Electron Affinity The energy change associated with the addition of an electron to a gaseous atom. X(g) + e  X(g) These values tend to be exothermic (energy released). Adding an electron to an atom causes it to give off energy. So the value for electron affinity will carry a negative sign.

Trends in Electronegativity.

Summary Quantum Numbers: Principal QN, Angular momentum QN, Magnetic QN, an Electron Spin QN. Orbital Shapes and Energies: s, p, and d orbitals. Pauli Exclusion Principle: Aufbau Principle: Hund’s Rule: Periodic Table: Periodic Trends: Atomic Radius Ionization Energy: Electron Affinity:

STOP End of Chapter 7