Atomic Structure. All matter is composed of atoms. Understanding the structure of atoms is critical to understanding the properties of matter.

Transcription

1 Atomic Structure

2 Atomic Structure All matter is composed of atoms. Understanding the structure of atoms is critical to understanding the properties of matter.

3 HISTORY OF THE ATOM suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS 1808 John Dalton

4 DALTONS ATOMIC THEORY 16X + 8Y 8X 2 Y

5 HISTORY OF THE ATOM found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON Joseph John Thompson

6 J.J. Thomson, measured mass/charge of e Nobel Prize in Physics

7 CHARGE OF AN ELECTRON 1909 Millikan oil drop experiment charges were all multiples of a certain base value, which was found to be C

8 HISTORY OF THE ATOM oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit 1910 Ernest Rutherford

9 Plum Pudding model of an atom

10 Rutherford s experiment

11 Results of foil experiment: if Plum Pudding model had been correct.

12 Actual Results

13 Rutherford s Model of the Atom atomic radius ~ 100 pm = 1 x m nuclear radius ~ 5 x 10-3 pm = 5 x m

14 A nuclear atom viewed in cross section

15 Atomic Structure Atoms are composed of -protons positively charged particles -neutrons neutral particles -electrons negatively charged particles Protons and neutrons are located in the nucleus. Electrons are found in orbitals surrounding the nucleus

16 Subatomic Particles Particle Mass(g) Charge(Coulombs) Charge(units) Electron (e-) 9.1 x x Proton (p) 1.67 x x Neutron (n) 1.67 x mass p = mass n = 1840 x mass e

17 HELIUM ATOM Shell

18 Atomic Structure Every different atom has a characteristic number of protons in the nucleus. atomic number = number of protons Atoms with the same atomic number have the same chemical properties and belong to the same element. Each proton and neutron has a mass of approximately 1 dalton. The sum of protons and neutrons is the atom s atomic mass. Isotopes atoms of the same element that have different atomic mass numbers due to different numbers of neutrons.

19 ATOMIC NUMBER (Z) = number of protons in nucleus MASS NUMBER (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons ISOTOPS atoms of the same element (X) with different numbers of neutrons

20 HISTORY OF THE ATOM 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 Niels Bohr

21 The Bohr Model of the Atom Shell

22 The Bohr Model of the Atom Ground and Excited States In the Bohr model of hydrogen, the lowest amount of energy hydrogen s one electron can have corresponds to being in the n = 1 orbit. We call this its ground state. When the atom gains energy, the electron leaps to a higher energy orbit. We call this an excited state. The atom is less stable in an excited state and so it will release the extra energy to return to the ground state. Either all at once or in several steps.

23 The Bohr Model of the Atom Hydrogen Spectrum Every hydrogen atom has identical orbits, so every hydrogen atom can undergo the same energy transitions. However, since the distances between the orbits in an atom are not all the same, no two leaps in an atom will have the same energy. The closer orbits are in energy, the lower energy of the photon emitted. Lower energy photon = longer wavelength. Therefore, emission spectrum has a lot of lines that are unique to hydrogen

24 Electromagnetic Spectrum

25 Every element has a unique emission spectrum Emission spectrum of Hydrogen

26 The Bohr Model of the Atom: Hydrogen Spectrum

27 ELECTRONS IN ORBIT ABOUT THE NUCLEUS

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29 ELECTRON DENSITY OF 1s ORBITAL

30 Schrödinger Wave Equation Ψ = fn(n, l, m l, m s ) n=principal quantum number for a given value of n, l = 0, 1, 2, 3, n-1 n = 1, l = 0 n = 2, l = 0 or 1 n = 3, l = 0, 1, or 2 Shape of the volume of space that the e- occupies l = 0 s orbital l = 1 p orbital l = 2 d orbital l = 3 f orbital

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33 Energy of orbitals in a single electron atom Energy depends only on principal quantum number n

34 Energy of orbitals in a many-electron atom Energy depends on n and l

35 Fill lowest energy orbitals first (Aufbau principle) He 2 electrons He 1s 2

36 Hund s rule: The most stable arrangement of electrons in subshells is one with the greatest number of parallel spins. O 8 electrons O 1s 2 2s 2 2p 4

37 2 8 octet 8 18

38 Outermost subshell being filled with electrons

39 Atomic Structure Neutral atoms have the same number of protons and electrons. Ions are charged atoms. -cations have more protons than electrons and are positively charged -anions have more electrons than protons and are negatively charged An ion is formed when an atom, or group of atoms, has a net positive or negative charge. If a neutral atom looses one or more electrons it becomes a cation. If a neutral atom gains one or more electrons it becomes an anion.

40 Electrons determine all of the chemical properties and some of the physical properties of elements.