ATOMIC STRUCTURE S.MORRIS 2006

(greek for indivisible) HISTORY OF THE ATOM Democritus develops the idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMOS (greek for indivisible)

384-322BC Aristotle and fellow Greeks According to him: According to him everything consisted of 4 elements, fire, water, earth, and air. His theory was accepted for a long period of time. Drawback: http://img.tfd.com/authors/aristotle.jpg

REGENTS QUESTION The concept that matter is composed of tiny, discrete particles is generally attributed to the (1)Romans (2) Germans (3) English (4) Greeks

HISTORY OF THE ATOM ATOMS John Dalton SOLID SHPERE MODEL 1808 Revisited Democritus’s idea suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

REGENTS QUESTION Dalton’s theory states that (1) All atoms of an element are positively charged (2) Different elements can have the same mass (3) Atoms of a given element must be identical (4) All atoms in a compound are identical

HISTORY OF THE ATOM ELECTRON Joseph John Thompson PLUM PUDDING OR RAISIN BUN MODEL 1898 Conducted Cathode ray tube experiment found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

PLUM PUDDING / RAISIN BUN HISTORY OF THE ATOM 1904 Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge like plums surrounded by pudding. PLUM PUDDING / RAISIN BUN MODEL

REGENTS QUESTION The first Subatomic Particle discovered was the (1) proton (2) electron (3) Neutron (4) photon

REGENTS QUESTION The discovery of the electron as a subatomic particle was a result of (1) Collision Theory (2) Kinetic Molecular Theory (3) Gold Foil experiment (4) Experiments with Cathode ray tubes

REGENTS QUESTION Which statement is consistent with the plum pudding model of the atom? (1) Electrons occupy regions of space (2) Negative particle orbit a positive nucleus (3) The atom consists of mostly empty space (4) Negative particles are embedded in atoms

HISTORY OF THE ATOM Ernest Rutherford 1910 EMPTY SPACE MODEL Performed the GOLD FOIL EXPERIMENT and discovered NUCLEUS

HISTORY OF THE ATOM Gold foil experiment helium nuclei Gold foil experiment He fired Helium nuclei at a piece of gold foil which was only a few atoms thick. They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nuclei bounced straight back.

HISTORY OF THE ATOM However, this was not the end of the story. Rutherford’s new evidence allowed him to propose a more detailed model with a central nucleus. He suggested that the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction However, this was not the end of the story.

REGENTS QUESTION After bombarding a gold foil sheet with alpha particles, scientists concluded that atoms consist mainly of (1) electrons (2) neutrons (3) empty space (4) protons

REGENTS QUESTION Experiments with gold foil indicate that atoms (1) usually have a uniform distribution of positive charges (2) usually have a uniform distribution of negative charges (3) contain a positively charged, dense center (4) contain a negatively charged, dense center

HISTORY OF THE ATOM Niels Bohr ORBIT MODEL / PLANETARY MODEL 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

Bohr’s Atom electrons in orbits nucleus

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

REGENTS QUESTION State one way in which the Bohr model agrees with the Thompson model. They both describe negatively charged electrons as part of their structure

1908 Robert Millikan He was by far the most famous American scientist. He proved electrons were negatively charged by performing an experiment where he measured effect of electric field on oil droplets. http://www.chemistryexplained.com/images/chfa_03_img0536.jpg

1920’s Electron Cloud Model Discovered by Erwin Schrödinger and Werner Heisenberg. They said an atom consists of a dense nucleus and many proton and neutrons and is surrounded by electrons, but they all have different energy levels, and different charges.

REGENTS QUESTION Modern Theory pictures an electron as (1) A Particle only (2) A wave only (3) Both a particle and a wave (4) Neither a particle nor a wave

1932 James Chadwick James discovered the existence of the neutron. He found this out because when he was looking at alpha waves(positive charge), bounced off the nucleus, saying there was no charge in the neutron. http://www.nuclearfiles.org/images/library/biographies/bio_chadwick-james.jpg

ATOMIC STRUCTURE Particle Charge Mass proton + charge 1 neutron No charge 1 electron - charge 1/1836th of a proton

number of electrons = number of protons ATOMIC STRUCTURE He 4 Atomic mass the number of protons and neutrons in an atom 2 Atomic number the number of protons in an atom number of electrons = number of protons

REGENTS QUESTION Find the number of neutrons in an atom of 79 Se 34 79 atomic mass – 34 atomic number= 45 neutrons

ISOTOPES of elements Atoms of the same element have the same atomic number (# of protons) and the same chemical properties. However, atoms of the same element may have different numbers of neutrons (and therefore different atomic mass) Isotopes are atoms of the same element having different number of neutrons

35Cl 37Cl 17 17 chlorine - 35 chlorine – 37 P = 17 P = 17 E = 17 E=17 17 17 chlorine - 35 chlorine – 37 P = 17 P = 17 E = 17 E=17 N = 18 N=18

Isotopes of Carbon Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #P __6_____ __6___ ___6____ #N ____6___ ___7____ ___8____ #E ____6___ ___6____ ___6____

REGENTS QUESTION ZINC PROBLEM An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom atomic number = 30 B. Number of neutrons in the zinc atom 65-30= 35 neutrons C. What is the mass number of a zinc isotope with 37 neutrons? 30 + 37= 67

Calculating AVERAGE ATOMIC MASS The mass numbers on the periodic table are the weighted average of the most abundant isotopes’ mass numbers. To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

Isotopes Mass of Isotope Abundance 24Mg = 24.0 amu 78.70% 25Mg = 25.0 amu 10.13% 26Mg = 26.0 amu 11.17% (24)(.787) + (25)(.1013) + 26(.1117) = 18.888 + 2.5325 + 2.9042 = 24.3 amu

Rubidium has two common isotopes, 85-Rb and 87-Rb Rubidium has two common isotopes, 85-Rb and 87-Rb. If the abundance of 85-Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium? 85 (.722) + 87 (.278)= 61.37 + 24.19 = 85.56 amu Isotopes Mass of Isotope Abundance Rb-85 = 85.0 amu 72.2% RB-87 = 87.0 amu 27.8%

1. Electronic Configuration ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1. Electronic Configuration 2. Dot & Cross Diagrams

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 2 in 1st shell 5 in 2nd shell 14 N 2 + 5 = 7 7

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

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

ELECTRONIC CONFIGURATION Of ATOMS excited state Write the electronic configuration for the following elements; Ca ( 2-8-8-2)  2-8-7-3 Na (2-8-1)  2-7-2 Cl ( 2-8-7)  2-7-8

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 14 X X N X X 7 X X

DOT & CROSS DIAGRAMS O Cl Draw the Dot & Cross diagrams for the following elements; X 16 35 X O Cl a) b) X 8 17 X X X X X X Cl X X X X X X X O X X X X X X X X X

THE BOHR MODEL GROUND STATE vs. EXCITED STATE electrons

Recall that a H-1 atom has one proton and no neutrons. Recall that a H-1 atom has one electron in the 1st shell when in the ground state. If a H-1 atom were to absorb a precise amount of energy, its electron could jump up to a higher energy electron shell. The electron is now said to be in an excited state

REGENTS QUESTION When electrons in an excited state fall to lower energy levels, energy is (1) absorbed (2) Released (3) Neither released or absorbed (4) Both released and absorbed

REGENTS QUESTION The Characteristic bright-line spectrum of an atom is produced when (1) Nuclei undergo fission (2) Nuclei undergo fusion (3) Electrons move from higher to lower energy levels (4) Electrons move from lower to higher energy levels

When do elements emit light in the form of color?

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.

ATOMIC structure AND ions Forming Ions: How it happens and how to draw it!

Valence electrons Valence electrons are those electrons that are lost or gained when elements combine

NON-METALS 17P 18N 17P = +17 18E= -18 ________ Nonmetals will gain electrons when forming compounds. They become negatively charged because there will be more electrons than protons. A negative ion will be formed. Cl 17P = +17 18E= -18 ________ ionic CHARGE 1E- = -1 17P 18N

METALS 11P 12N 11P = +11 10E = -10 ________ IONIC charge 1P = +1 Metals will lose electrons when forming compounds. They become positively charged because there will be more protons than electrons. A positive ion is formed Na⁺ 11P = +11 10E = -10 ________ IONIC charge 1P = +1

Sodium loses one electron Sodium loses one electron. Sodium now has 11 protons and 10 electrons, (+1). Chlorine gains one electron. Chlorine now has 17 protons and 18 electrons, (-1).

Valence electrons are electrons that are lost or gained when elements combine. Ions are elements that lose or gain an electron. They then become electrically charged, therefore electrically attractive and open for bonding!

Elements in Group 1 will lose 1 electrons and become positive (+1) ions. Elements in Group 2 will lose 2 electrons and become positive (+2) ions. Elements in Group 13 will lose 3 electrons and become positive (+3) ions. Elements in Group 14 can either lose or gain 4 electrons, either (+/-4) ions.

Elements in Group 15 will gain 3 electrons and become negative (-3) ions. Elements in Group 16 will gain 2 electrons and become negative (-2) ions. Elements in Group 17 will gain 1 electron and become negative (-1) ions.