Atomic Structure. Defining the Atom. Defining the Atom. Sizing up the Atom. Structure of the Atom 9/18/2012

Transcription

1 Atomic Structure Defining the Atom Atom smallest particle of an that retains the chemical of that element 1 2 Defining the Atom The Greek philosopher Democritus (460 B.C. 370 B.C.) was among the to suggest the existence of ( atomos (from the Greek word He believed that atoms were indivisible and indestructible His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method but just 3 (! based Dalton s Atomic Theory (experiment John Dalton ( ) 1) All elements are composed of tiny indivisible particles called 2) Atoms of the same element are. Atoms of any one element are from those of any other element. 1) Atoms of different elements combine in simple whole-number ratios to form chemical 2) In chemical reactions, atoms are combined, separated, or rearranged but changed into atoms of another element. 4 Sizing up the Atom Elements are able to be subdivided into smaller and smaller particles these are the, and they still have of that element If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long Despite their small size, individual atoms are observable with instruments such as scanning tunneling (electron) Structure of the Atom One change to Dalton s atomic theory is that atoms are into subatomic particles:,, and are examples of these fundamental particles There are many other types of particles, but we will study these three microscopes 5 6 1

2 Thomson s Atomic Model J. J. Thomson Thomson believed that the electrons were like plums embedded in a charged pudding, thus it was called the pudding 7 model. Although Thompson had the positive and negative particles in the wrong place, he is credited with discovering. 8 Earnest Rutherford s Experiments Conclusions: a) The nucleus is b) The nucleus is c) The nucleus is charged This fixed Thompson s plum pudding model. Rutherford is credited with discovering the The Rutherford Atomic Model Based on his experimental evidence: The atom is mostly space All the positive charge, and almost all the is concentrated in a small area in the. He called this a nucleus The nucleus is composed of and (! nucleus (they make the The distributed around the nucleus, and occupy most of the His model was called a nuclear model Bohr Model Neils Bohr discovered of electrons. He said that electrons orbited the nucleus like planets orbit the he was wrong about the orbiting but right that there are particular energy levels that electrons reside in. Modern (Wave) Model of the Atom The modern model of the atom consists of that electrons move around in we will discuss later

3 About Atoms There are presently elements, thus 118 kinds of. These atoms in many different combinations and proportions to form the tremendous number of found. Experiments determined that atoms contain three particles: protons, neutrons, and electrons. 13 Atoms have a positively charged dense central core called a nucleus. The nucleus contains protons and neutrons. Protons charge Neutrons or zero charge Protons and neutrons have about the same mass. Electrons move in the space around the nucleus called the. Electrons charge Electron s mass is than that of neutrons and protons. 14 The nucleus is much more but much than the electron cloud. If you made a model of an atom to scale use as nucleus, the end of the atom would be 2 fields away from the baseball. abbreviations commonly used: p +, n o, e - 15 Particle Electron (e - ) Proton (p + ) Neutron (n o ) Subatomic Particles Charge Mass (g) and Mass (amu) 9.11 x g Approx. _ amu x g amu x g amu 16 Location Atomic Number tells the number of in an atom. It is found on the periodic table. Ex: there are protons in an atom of Nitrogen, there are protons in an atom of Uranium The number of in an atom makes the atom what it is! Ex. Potassium has 19 protons it can never have any more or any less and still be potassium. Individual atoms are electrically, which means they have the number of as. Ex. An atom of copper has protons and electrons. 17 Mass Number of and of a particular atom. Ex. Chlorine-37 Ex. Aluminum-27 Atomic number: Atomic number: Mass number: Mass number: p+: p+: e-: e-: no: no: 18 3

4 Naming Isotopes The number written after an element name is always the number for a particular isotope of that atom. carbon-12 carbon-14 uranium Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p + + n 0 Nuclide Oxygen - 18 Arsenic - 75 Phosphorus - 31 p + n 0 e - 20 Mass # Question: Why do you think the mass number only includes protons and neutrons? Answer: because protons and neutrons both have a mass of amu, but electrons have a mass of amu Question: Why do you think the mass number is always a whole number? Answer: because there are always numbers of protons and neutrons in an atom 21 Complete Symbols Contain the symbol of the element, the mass number and the atomic number. Mass number Superscript Subscript Atomic number X 22 Symbols Find each of these: number of protons number of neutrons number of electrons Atomic number Mass Number Br 23 Symbols If an element has an atomic number of 34 and a mass number of 78, what is the: number of protons number of neutrons number of electrons complete symbol 24 4

5 Symbols If an element has 91 protons and 140 neutrons what is the Atomic number Mass number number of electrons Symbols If an element has 78 electrons and 117 neutrons what is the Atomic number Mass number number of protons complete symbol 25 complete symbol 26 Isotopes Dalton was wrong about all elements of the same type being Atoms of the same element can have numbers of. Thus, different numbers. These are called isotopes atoms with the same number of protons but different number of neutrons...thus they have different masses. 27 Isotopes Elements occur in as of isotopes. Ex. Chlorine exists as chlorine- and chlorine-. Both have protons but one has neutrons and one has neutrons. There is no way of predicting which isotopes exist for each element; these have been determined. 28 Atomic Mass How heavy is an atom of oxygen? It depends, because there are different of oxygen atoms. We are more concerned with the average atomic mass. (this number is found on the ( This is based on the (percentage) of each variety of that element in. We don t use for this mass because the numbers would be too small. 29 Measuring Atomic Mass Instead of grams, the unit we use ( ) is the Atomic Mass Unit Each isotope has its own atomic mass, thus we determine the average from percent abundance, which is why it is a and not a number. 30 5

6 Atomic Masses Atomic mass is the average of all the naturally occurring isotopes of that element. Isotope Carbon-12 Carbon-13 Carbon-14 Symbol 12 C 13 C 14 C Composition of the nucleus 6 protons 6 neutrons 6 protons 7 neutrons 6 protons 8 neutrons % in nature 98.89% 1.11% <0.01% To get the most mass number, the atomic mass off to the nearest whole number. Example: What is the most common mass number of the following? Ag, Cu, C, Cl Carbon = Draw models of lithium-5, lithium-6, and lithium-7 atoms including the correct numbers of protons, neutrons, and electrons in each. 33 IONS Ion atom that has or electrons Two types: a positive ion, one that has electrons a negative ion, one that has electrons Atoms NEVER gain or lose or ( reactions (except in nuclear 34 Examples Examples: Mg is a magnesium atom and has protons and electrons so the overall charge is. Mg +2 is a magnesium ion and has protons and electrons so the overall charge is. Cl is a chlorine atom and has protons and electrons so the overall charge is. Cl - is a chlorine ion has protons and electrons so the overall charge is

7 Energy Levels Maximum number of electrons Who was the first to notice that the electron cloud has different regions where electrons reside? There are various in an electron cloud. Within each energy level there are and within each sublevel there are. Each orbital can hold up to two electrons. Electrons move very within their own. Energy levels (n) can hold a maximum number of 2n 2 electrons. Energy level Max num of e More about energy levels The total number of levels an atom has corresponds to the number of the atom. Periods are the rows on the PT Ex. An atom of bromine has energy levels because it is in period The energy level, called the shell, can hold ONLY up to electrons. Valence Electrons electrons are the electrons in the energy level. The atoms are arranged on the periodic table so that the ones with properties all line up in a or. The of valence electrons plays a big role in how the atom Group Number 1 (1A) 2 (2A) 3-12 and the actinides and lanthanides (B s) 13 (3A) 14 (4A) 15 (5A) 16 (6A) 17 (7A) 18 (8A) Number of Valence e- Except He (2) 41 Electron dot diagrams Use the number of valence electrons as and space them around the sides of the element s symbol then up as needed Examples: 42 7

8 Group/Family Names to Label Alkali Metals Alkaline Earth Metals Transition Metals Lanthanides Actinides Boron Family Carbon Family Nitrogen Family Oxygen Family Halogens Noble Gases Periods Ion Charge Prediction Octet rule atoms will, or share electrons so that they have a shell That's electrons for everything except 1 st shell (H and He) which only holds electrons Ex. Nitrogen has valence electrons so it will gain to make. N -3 Ex. Sodium has valence electron so it will lose that one and the shell becomes the valence shell with electrons. Na

9 Group 1 (1A) makes Group 2 (2A) makes Group 3-12 (B's) are Group 13 (3A) makes Group 14 (4A) makes Group 15 (5A) makes Group 16 (6A) makes Group 17 (7A) makes Group 18 (8A) makes (doesn't form ions!) why? Examples: Electron Configurations AUFBAU principle electrons fill orbitals starting with the energy orbital available before filling higher energy orbitals. PAULI EXCLUSION principle each orbital can hold at most _ electrons and they must have ( couterclockwise spins (clockwise and HUND'S rule electrons occupy equal-energy orbitals so that a maximum number of electrons results ex. not **spread out before pairing up** 51 Sublevels: s, p, d and f 52 Orbitals

10 55 56 Writing electron configurations Use the periodic table as a guide

11 More Electron Configurations Abbreviated Electron Configurations Use the previous to shorten the electron configuration Orbital Notation Use to represent electrons. Exceptions to Orbital Fill Order Any electron configuration that ends in is too and actually takes an electron from the previous sublevel and becomes. Example: Another Exception Examples: Any electron configuration that ends in is too and actually takes an electron from the previous sublevel and becomes. Example:

12 Absorption and Emission Normally, electrons in an atom are in the state, which means they are in the possible energy levels. However, these electrons can be to higher energy levels if energy is added...called. If energy is absorbed and the electrons jump to higher energy levels they are now in the state. 67 Once in the excited state the atoms are and thus energy when they fall back down to their original energy levels. This process is called. This of absorption and emission happens very fast over and over again. Atoms can be excited using, light, or electricity. Emission is usually in the form of. Different energies of light have different. The light spectrum: ( energy (lower energy)roygbiv (higher 68 This is actually how we see colors! 69 12