Topic: Modern Atomic Theory

Topic: Modern Atomic Theory

TOPIC: MODERN ATOMIC THEORY ESSENTIAL QUESTION: HOW DID THE EXPERIMENTS OF SCIENTISTS OVERTIME DEVELOP THE MODERN ATOMIC THEORY? BY THE END OF THE LESSON YOU SHOULD BE ABLE TO 1. List the names of Scientists who helped with the study of the Atom and explain what they contributed. 2. Explain energy levels & why certain elements emit different colors of lights in fireworks.

3. Explain what are orbitals and electron configurations. 4. Describe the difference between ground and excited states of electrons. MI#1: GREEK MODELS Democritus Believed that all matter consisted of extremely small particles that could not be divided. Termed the word Atoms or atomos which means uncut or indivisible.

MI#1: GREEK MODELS Aristotle Didnt think there was a limit to the number of times matter could be divided. Thought that all substances were built up from only four elements (Earth, Air, Fire & Water). His theory was accepted for many centuries till the 1800s when the

Atomic model of matter was created. MI#2: DALTONS ATOMIC THEORY Teacher, born in England in 1766 who spent spare time doing scientific experiments. Discovered the existence of atoms by measuring masses of elements that combine when compounds form.

MI#2: DALTONS ATOMIC THEORY Dalton proposed a theory that all matter is made up of individual particles called atoms, which cannot be divided. MI#3: DALTONS THEORY Daltons Theory All elements are composed of atoms

All atoms of the same element have the same mass and atoms of different elements have different masses Compounds contains atoms of more than one element In a particular compound, atoms of different elements always combine in the same way MI#4: THOMSONS MODEL OF THE ATOM J.J. Thomson (1856-1940) used an electric current to learn more about atoms. Experiments involved sealed tubes of

gas with two oppositely charged disks on either side. These experiments provided the first evidence that atoms are made of even smaller particles and can be divided into subatomic particles. MI#4: THOMSONS MODEL OF THE ATOM Thomsons Model Plum Pudding Model Negative charges are evenly

scattered throughout an atom filled with a positively charged mass of matter (resembles a chocolate chip ice cookie) MI#5: RUTHERFORDS ATOMIC THEORY In 1909 Ernest Rutherford asked a student to find out what happens to alpha particles when they pass through a thin sheet of gold

Discovered that the positive charge of an atom is not evenly spread throughout the atom. MI#5: RUTHERFORDS ATOMIC THEORY Positive charges are concentrated in a small central area called the nucleus Nucleus is dense and found in the center of an atom

MI#6: BOHRS MODEL OF THE ATOM Niels Bohr (1885-1962) , a Danish physicist who worked for a while with Rutherford created the Bohr Model. In Bohrs model, the electrons move with constant speed in fixed orbits around the nucleus. MI#6: BOHRS MODEL OF THE ATOM

Each electron has a specific amount of energy and can be gained or lost. Energy levels= the possible energies that electrons in an atom can have MI#7: ENERGY LEVELS Like steps in a staircase, an electron in an atom can move from one energy level to

another. Can move up energy levels if it gains enough energy. Can move down energy levels if it loses enough energy. MI#7: ENERGY LEVELS The size of the jump determines that amount of energy gained or lost.

MI#7: ENERGY LEVELS The movement of electrons between energy levels explain the light you see when fireworks explode. Heat from the explosion causes some electrons to move to higher energy levels, when they move back down they emit some energy as visible light. Different elements emit different colors of light.

MI#8: ELECTRON CLOUD MODEL Electron cloud= a visual model of the most likely locations of electrons in an atom around the nucleus Denser in locations where the probability of finding an electron is high MI#9: ENERGY LEVELS, ORBITALS & ELECTRONS

The electron cloud represents all the orbitals in an atom. Orbital= a region of space around the nucleus where an electron is likely to be found MI#9: ENERGY LEVELS, ORBITALS & ELECTRONS The level in which an electron has the least energy (lowest energy level) has only 1 orbital.

Higher energy levels have more than 1 orbital. The first 4 energy levels of an atom: Max # of electrons by level (1=2, 2=8, 3=18, =32) Levels start from the nucleus out Bohrs Atomic Orbit MI#10: ELECTRON CONFIGURATIONS

First Electron Configurations= Second the arrangement of Third Fourth electrons in the orbitals of Fifth an atom Sixth The most stable electron

Seventh configuration is the one in which the electrons are in the orbitals with the lowest energies. Quantum # n=1 n=2

n=3 n=1 n=2 n=3 n=7 Atomic Energy Level 1 2

3 4 5 6 7 MI#10: ELECTRON CONFIGURATIONS Ground State= when all the energies in an atom have the lowest possible energies, most stable

Excited State= when an electron is in an orbital with a higher energy level, less stable than the ground state WHERE ARE YOU NOW ARE YOU ABLE TO 1. List the names of Scientists who helped with the study of the Atom and explain what they contributed. 2. Explain energy levels & why certain elements emit different colors of lights in fireworks.

3. Explain what are orbitals and electron configurations. 4. Describe the difference between ground and excited states of electrons. CHECKING FOR UNDERSTANDING 1. Bohrs model shows what about electrons? 2. Explain how different colors of lights are created in fireworks. 3.Explain the difference between the ground state and excited state of an electron.

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