ATOMIC STRUCTURE

Bohr’s Atom electrons in orbits nucleus

What is an atom? Atom: the smallest unit of matter that retains the identity of the substance

Atomic Structure Atoms are composed of 2 regions: Nucleus: the center of the atom that contains the mass of the atom Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Nucleus Electron Cloud

What’s in the Nucleus? The nucleus contains 2 of the 3 subatomic particles: Protons: positively charged subatomic particles Neutrons: neutrally charged subatomic particles

HELIUM ATOM + - + - Shell proton neutron electron What do these particles consist of?

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

What’s in the Electron Cloud? The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic particle with a negative charge and relatively no mass

How do these particles interact? Protons and neutrons live compacted in the tiny positively charged nucleus They account most of the mass of the atom The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus

How do the subatomic particles balance each other? In an atom: The protons = the electrons If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom—atoms are neutral The neutrons have no charge;

How do we know the number of subatomic particles in an atom? Atomic number: this number indicates the number of protons in an atom Ex: Hydrogen’s atomic number is 1 So hydrogen has 1 proton Ex: Carbon’s atomic number is 6 So carbon has 6 protons **The number of protons identifies the atom. Ex. 2 protons = He, 29 protons = Cu

How do we know the number of subatomic particles in an atom? Mass number: the number of protons and neutrons in the nucleus Ex: oxygene can have a mass of 16. Since it has 8 proton it must have 8 neutrons

What about the electrons? The electrons are equal to the number of protons Ex: O has a mass of 16 and an atomic number of 8 and has 8 electrons.

What about the electrons? Model of the atom pictures the electrons moving around the nucleus in a region called an electron cloud. The electron cloud is a cloud of varying density surrounding the nucleus.

What about the electrons? Electrons are found in specific circular paths (orbits) around the nucleus. The electrons have fixed energies called energy levels. (like rungs on a ladder) The amount of energy required to move an electron to another energy level is called a quantum (shell). The energy levels of electrons are labeled by principal quantum numbers (n)

ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. first shell a maximum of 2 electrons second shell a maximum of 8 electrons third shell a maximum of 8 electrons

How exactly are the particles arranged? Bohr Model of the atom: All of the protons and the neutrons The 3rd ring can hold up to 18 e- The 1st ring can hold up to 2 e- The 4th ring and any after can hold up to 32 e- The 2nd ring can hold up to 8 e-

What does carbon look like? Mass number = 12 Atomic number = 6 p+ = 6 no = 6 e- = 6 6 p and 6 n live in the nucleus

ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; Nitrogen configuration = 2 , 5 7 2 in 1st shell 5 in 2nd shell N 2 + 5 = 7 14

ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; 20 11 8 Na O Ca a) b) c) 16 23 40 1s2,8,8,2 2,8,1 2,6 17 14 5 Cl Si B d) e) f) 11 35 28 2,8,7 2,8,4 2,3

N DOT & CROSS DIAGRAMS Nitrogen With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X Nitrogen N 7 X X N X X 14 X X

DOT & CROSS DIAGRAMS O Cl X X X X X X X X X Cl X X X X X X X O X X X X 8 17 X O Cl a) b) X 35 X 16 X X X X X Cl X X X X X X X O X X X X X X X X X X

How is the dispertion of electrons in shell? The outer energy level or “shell” is considered full when it has the maximum number of electrons that can fit into that level.

How is the dispertion of electrons in shell? The outer energy level or “shell” is considered full when it has the maximum number of electrons that can fit into that level. For example, the 1st level is full when it has 2 electrons, but the 2nd and 3rd levels are full when it has 8 electrons.)

How is the dispertion of electrons in shell? If the outside energy level is full, it is considered non-reactive. It does not need to chemically react or bond with any other atom or molecule.

How is the dispertion of electrons in shell? If the outside energy level is full, it is considered non-reactive. It does not need to chemically react or bond with any other atom or molecule. If the outside energy level is incomplete (not full), it is considered reactive.

How is the dispertion of electrons in shell? If the outside energy level is full, it is considered non-reactive. It does not need to chemically react or bond with any other atom or molecule. If the outside energy level is incomplete (not full), it is considered reactive. It will either lose or gain electrons and chemically react or bond with another atom or molecule.

Orbitals The electrons of an atom are in constant motion .

Orbitals The electrons of an atom are in constant motion . The region of space that an electron occupies is known as an ORBİTAL.

Orbitals The electrons of an atom are in constant motion . The region of space that an electron occupies is known as an ORBİTAL. Orbital comprise sublevels of a principal energy level. The sublevels are named as s, p, d, f.

Orbitals Each sublevels containes a different number of electrons. s = 1 orbital d = 5 orbitals p = 3 orbitals f = 7 orbitals

Orbitals Each sublevels containes a different number of electrons. s = 1 orbital d = 5 orbitals p = 3 orbitals f = 7 orbitals s and p orbitals most important in organic and biological chemistry

Orbitals Each sublevels containes a different number of electrons. s = 1 orbital d = 5 orbitals p = 3 orbitals f = 7 orbitals s and p orbitals most important in organic and biological chemistry s orbitals: spherical, nucleus at center p orbitals: dumbbell-shaped, nucleus at middle d orbitals: elongated dumbbell-shaped, nucleus at center

Sublevels continued The maximum number of electrons allowed in each sublevel are as follows: s = max 2 electrons p = max 6 electrons d = max 10 electrons f = max 14 electrons

Orbitals

Orbitals Orbital are grouped in shells of increasing size and energy

Orbitals Orbital are grouped in shells of increasing size and energy Different shells contain different numbers and kinds of orbitals Each orbital can be occupied by two electrons.

Orbitals Orbital are grouped in shells of increasing size and energy Different shells contain different numbers and kinds of orbitals Each orbital can be occupied by two electrons.

SUMMARY The Atomic Number of an atom = number of protons in the nucleus. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. The number of Protons = Number of Electrons. Electrons orbit the nucleus in shells. Each shell can only carry a set number of electrons.