Atomic Structure

1. Atomic Structure Topic 1

2. Objectives: • To understand how the model of the atom has changed • To know the subatomic particles and all their properties • To understand electrons and their energies • To be able to distinguish between ground, excited state and ion configurations • To distinguish between different types of matter

3. Early Studies of Matter • The model of the atom is the work of many scientists over a long period of time • Greeks • Fire, air, water, and earth • Boyle – 1600s • Gold and silver are elemental

4. Dalton – 1700s • Atom = basic unit of matter • cannonball • Dalton’s Atomic Theory • All elements are composed of indivisible atoms • All atoms of a given element are identical • Atoms of different elements are different; (different masses) • Compounds are formed by the combination of atoms of different elements • Not all correct today but the groundwork

5. Thomson – “Plum Pudding” • Electron • Atom has some negative charged particle found within

6. Rutherford’s Gold Foil Experiment • Nucleus of atom discovered • Nuclear model • Experiment: • Alpha particle shot at a piece of gold foil

7. Rutherford’s Gold Foil Experiment

8. Bohr Model • Planetary model • Electrons in definite fixed orbits • How we draw them

9. Wave-Mechanical Model • Most modern model of the atom • Gives electrons properties of both particle and wave • Electrons with distinct amounts of energy moving in orbitals • Orbitals = region in which electron is likely to be located

10. Structure of the Atom • Positive nucleus and negative electrons in regions called orbitals outside nucleus

11. Atomic Number • Atomic Number is the number of protons Atomic number = # protons • Each element has its own atomic number…it identifies what element you have

12. Complete Chart

13. Atom is neutral • Neutral means equal amount of positive and equal amount of negative • SOOO…. WHAT 2 SUBATOMIC PARTICLES WILL BE EQUAL IN AN ATOM? • Remember: APE

14. Mass Number • Mass number is the mass of the nucleus (protons + neutrons) Mass # = #protons + #neutrons Mass # - #protons = #neutrons • Notation: C-12 126C

15. Complete Chart

16. Isotopes • Isotopes are atoms of the same element that have different numbers of neutrons (giving them different mass numbers) • Same: #protons (atomic numbers) • Different: #neutrons (mass numbers)

17. Atomic Masses • Average masses of all the naturally occurring isotopes • Weighted average

18. Finding Atomic Mass Problems • Carbon has 2 naturally occurring isotopes. 98.89% of C’s are C-12 with a mass of 12 amu. The remaining 1.108% are C-13 with a mass of 13 amu. What is the atomic mass of carbon?

19. Sample Problem Element X three isotopes; one that occurs 72.0% with a mass of 84.9 amu, the second that occurs 18.0% with a mass of 87.0 amu, and the last that occurs 10% with a mass of 89.1 amu. Find the average atomic mass of Element X.

20. Solution

21. Electrons, Electrons, Electrons • Electrons surround the nucleus in regions called orbitals • Electron Configurations for the atom are on the reference tables • Tells how many electrons are in each energy level • Last number in electron configuration is number of valence electrons (outermost electrons)

22. Sample Questions • Write the electron configuration of the following atoms: • Sodium • Chlorine • Fe • Circle the valence electrons in the above atoms

23. Energy of Electrons • Each electron has its own distinct amount of energy that corresponds to the energy level that it occupies • Higher the energy level the higher the electron’s energy

24. Ground vs. Excited State • Electrons can gain or lose energy making them move to higher or lower energy levels • Ground State: electrons in their normal energy levels; stable • Found on the reference table • Excited State: electron gains energy and moves up to a higher energy level • Start with configuration on table, keep same number electrons, but change the order

25. Continued • Ground  Excited; energy is __________ • Excited  Ground; energy is __________ • Calcium atom’s electron configuration is… • Ground state: • Excited state:

26. Sample Problems

27. Sample Problems • Which shows an increase in energy? A - Electron that goes from the 2nd shell to the 3rd shell B - Electron that goes from the 3rd shell to the 2nd shell • Which of the above A or B will produce a light spectrum?

28. Ionic Radii

29. Types of Matter • Matter – anything that has mass and takes up space (volume) • Homogeneous – uniform composition • Can contain more than one type of particle, but the particles have to be evenly mixed • Sugar water • Heterogeneous – varying composition • Parts have there own chem and phys properties • Chocolate chip cookie

30. Matter Pure Substance Mixtures All other heter. mixs Compound Element Solutions

31. Definitions • Pure Substances – composition is the same throughout • Element – substances that cannot be broken down or decomposed into simpler substances by chemical means

32. Compounds – two or more elements that are chemically combined in definite proportions by mass • Law of definite proportions – types of atoms in a compound exist in a fixed ratio • H2O2 vs. H2O • H2O: mass ratio of 1:8

33. Mixtures – combinations of two or more pure substances that can be separated by physical means (not in “fixed” ratios) • Heterogeneous mixtures • Homogenous mixtures = solutions