Atomic Structure - 2 - PDF

Atom structure Learning objectives:  Describe the structure of an atom.  Identify three types of subatomic particles.  Define atomic and mass number.  Calculate the atomic mass of an element.  Explain what makes elements and isotopes different from each other Atomic Theory:...

Atom structure Learning objectives:  Describe the structure of an atom.  Identify three types of subatomic particles.  Define atomic and mass number.  Calculate the atomic mass of an element.  Explain what makes elements and isotopes different from each other Atomic Theory:  Atoms are the building blocks of all matter.  Matter is anything that takes up space and has mass.  Understanding the structure of atoms is critical to understanding the properties of matter subatomic particles  The smaller parts that make up atoms are called subatomic particles.  Many types of subatomic particles have since been discovered.  The three particles that are most important for chemistry are the electron, the proton, and the neutron. Properties of an electron, a Proton and a Neutron Name Symbol Charge Common Mass (kg) charge Electron e, e−, or −1.602 × −1 9.109 × 0e 10−19 10−31 −1 Proton p, p+, or +1.602 × +1 1.673 × 1p 10−19 10−27 +1 Neutron n or 0 1 n 0C 0 1.675 × 10−27 In an atom  Thenumber of protons = the number of electrons  If20 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; therefore they do not have to equal the number of protons or electrons Atomic number  Atomic number: Indicates the number of protons in an atom Ex: Hydrogen’s atomic number is 1 So hydrogen has 1 proton **The number of protons identifies the atom. Ex. 2 protons = He, 29 protons = Mass number  Mass number: the number of protons and neutrons in the nucleus Ex: hydrogen can have a mass of 3. Since it has 1 proton it must have 2 neutrons Number of neutrons = Mass number - Atomic number Determine the number of subatomic particles in the following: Atom Mass Atomic P+ no e- number number Li 7 3 3 4 3 Ne 20 10 Cl 35 17 K 39 19 C 13 6  How do these particles arranged in an atom? (atomic structure)  Bohr’s Model  Atom has a positively charged central part (nucleus)  Massof an atom is concentrated at nucleus (proton and neutron)  Electronscan be only at certain distances (orbit) from the nucleus.  Each orbit can hold a specific maximum number of electrons (2n2 ). Bohr Model of the atom (2n2): Energy Levels Nucleus (protons and The 3rd the orbit can neutrons) hold up The 1st orbit to 18 e- can hold up to 2 e- The 2nd orbit can hold up to 8 e- The Electron Cloud model  Is a probability model  Describes a cloud like region called orbital where the electron is likely to be.  Based on mathematical equation The Electron Cloud model Quantum Numbers To define the region in which electrons can be found, scientists have assigned four quantum Numbers to each electron: 1. Principal quantum number (n) indicates the main energy level occupied by the electron. Values of n are positive integers, such as 1, 2, 3, and 4. 2. Angular momentum quantum number (L) represent sublevels (s, p, d, f, ….), indicates the shape or type of orbital. Values 0, 1,……,n-1. 3. Magnetic quantum number (m) indicates the numbers and orientations of orbitals around the nucleus values –L, 0, +L Quantum Numbers Quantum Symbo Values Indicates Number l Principal n 1, 2, 3, 4, …. Main energy level Angular L 0, 1, 2, ……, Sublevels (shape or momentum n-1 type) Magnetic m -L, 0, +L numbers and orientations of orbitals Spin s +1/2, -1/2 Spin Angular momentum Sublevels name quantum number 0 s 1 p 2 d 3 f Quantum Numbers of the First 30 Atomic Orbitals n L m Orbital name Number of (0 – n-1) (-L, …, 0, ….. +L) orbitals 1 0 0 s 1 2 3 4 Electrons Configuration Is the arrangement of electrons in an atom. Each energy level can hold 2n2 electrons (n = 1,2,3,4......) energy levels are divided into sublevels called orbitals, which are designated by the letters s, p, d, f,........ Electron Configurations  Aufbau Principle: orbitals fill in order of increasing energy from lowest energy to highest energy  Pauli Exclusion Principle: only two electrons can occupy an orbital and their spins must be paired  Hund’s Rule: when orbitals of equal energy are available but there are not enough electrons to fill all of them, one electron is added to each orbital before a second electron is added to Electron Configurations  Example: Carbon’s atomic number is 6 Bohr’s Model: 2, 4 The Electron Cloud model: 2p energy 2s 1s Isotope  An atom that has the same number of protons (atomic number) but has a different number of neutrons (atomic mass). Elements  Element is a substance composed of a single kind of atom.  Scientists have identified 90 naturally occurring elements, and created about 28 others(118).  The elements, alone or in combinations, make up our bodies, our world, our sun, and in fact, the entire universe. How are elements organized? Reference  HOLT chemistry(2006) R. Thomas Myers, Keith B. Oldham and Salvatore Tocci. Holt, Rinehart and Winston.  Introduction to organic chemistry and biochemistry.  Internet.