Notes 4-1

Intro to AtomsNotes 4-1Lets see how much you remember.Chapter Preview Questions1. Groups of two or more atoms held together by chemical bonds area. elements.b. molecules.c. particles.d. electrons.3

Chapter Preview Questions1. Groups of two or more atoms held together by chemical bonds area. elements.b. molecules.c. particles.d. electrons.4Chapter Preview Questions2. When elements are chemically combined in a set ratio, they form a. molecules.b. matter.c. elements.d. compounds.5

Chapter Preview Questions2. When elements are chemically combined in a set ratio, they form a. molecules.b. matter.c. elements.d. compounds.6Chapter Preview Questions3. Which of the following is an example of an element?a. copperb. rustc. concreted. water7

Chapter Preview Questions3. Which of the following is an example of an element?a. copperb. rustc. concreted. water8Chapter Preview Questions4. Two compounds with different properties are a. C and O.b. H and O.c. CO and CO2.d. Cl and Ar.9

Chapter Preview Questions4. Two compounds with different properties are a. C and O.b. H and O.c. CO and CO2.d. Cl and Ar.10Whats an atom?Smallest particle of an element

Atomic TheoriesThere have been many theories of proposed models of the atom.Some were completely wrong!And some were partially correct or close to correct.We will look at some of the most known theories and models.Daltons Atomic TheoryDalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces.He was credited with coming up with the earliest model of the atomMost of this theory is still accepted today

13Thomsons ModelThomson suggested that atoms had negatively charged electrons embedded in a positive sphere.This is the first model that included smaller particles of the atom His model is similar to blueberries in a muffin

14Rutherfords ModelDeveloped the first model that included a nucleusSimilar to a peach with a pit, the pit = the heavy mass of protons in the nucleus, the fruit = the empty space made up of electrons

Rutherfords Gold Foil ExperimentTurn to page 126-127 in your text bookLets read about Rutherfords model/ experimentWho wants to read first?Everyone else, follow along.Rutherfords Gold Foil ExperimentRutherford was surprised that a few particles were deflected strongly. This led him to propose an atomic model with a positively charged nucleus.

17Bohrs ModelSaid electrons could only have a certain amount of energy, so they must move in certain orbitsSimilar to planets orbiting the sun (sun = nucleus), or the rings/layers of an onion

Cloud ModelSays Bohrs model is wrong, electrons do not orbit the nucleus like planets do the sunInstead, electrons can be found anywhere in a cloud-like region around the nucleus, rapidly orbiting in every direction

Later Atomic ModelsThrough the first part of the twentieth century, atomic models continued to change.

20Modern Atomic ModelAccepted since the 1930sAt the center of the atom is a massive nucleus, containing positively charged protons and neutrally charged neutrons (no charge)Surrounding the nucleus is a cloud-like region of moving negatively charged electrons# protons in atom = # electrons in atom# neutrons can changeParticles in an AtomAn atom is composed of positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are about equal in mass. An electron has about 1/2,000 the mass of a proton or neutron.

22Atomic NumberEvery atom of a given element has the same number of protons in its nucleusThis is known as the elements atomic numberFor example, Heliums atomic number is 2, so every atom of helium has 2 protons in its nucleus. If the element has more than 2 protons, it is NOT helium!Carbons atomic number is 6. How many protons does an atom of carbon have?Atomic NumberThe atomic number is usually found above the letter on the periodic tableLook at helium below

Isotopes: Atoms of elements have same number of protons, but different numbers of neutronsAtoms of all isotopes of carbon contain six protons and six electrons, but they differ in their number of neutrons. Carbon-12 is the most common isotope.

25Mass numberAn isotope is identified by its mass numberMass number = #protons + #neutronsExample: Carbon-12, the mass number is 12. We know carbon has 6 protons by looking at its atomic number on the periodic table. How many neutrons does carbon-12 have?6How do you know?Because if the mass number is 12, 12 - 6protons = 6neutronsProblem:The atomic number of nitrogen is 7. How many protons, neutrons, and electrons make up Nitrogen-15?Protons = 7Neutrons = 8Electrons = 74-2 NotesOrganizing the ElementsMendeleevs Periodic Table1869 Russian scientist who discovered a pattern of the elementsArranged the elements in order of increasing atomic mass (average mass of all the isotopes of an element)Then he lined them up in groups of similar propertiesDeveloped the first periodic table of elementsContained 63 elementsThe Modern Periodic TableChanged as new elements were discoveredContains over 100 elementsArranged in order of increasing atomic number (not atomic mass like Mendeleevs)Atomic number = number of protons in an atom of that elementThe properties of an element can be predicted from its location on the periodic table

The Periodic TableElements are organized into rows and columns based on their atomic number.

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The Periodic TableElements are organized into rows and columns based on their atomic number.

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The Periodic TableElements are organized into rows and columns based on their atomic number.

33Classes of ElementsOpen your books to pages 134-135Each colored region corresponds to a different class of elementsMetals = blueSemimetals = yellowNonmetals = light greenInert gases = dark greenPeriods Horizontal rowsThere are 7 periods on the table, look how they are labeled on the left side of the tableProperties within each period change in a patternNotice the lanthanides and actinides have been taken out of the table and placed underneath itThis is to save space and make the table easier to readLook at the expanded table on page 136Groups Vertical columnsAka familyElements within the same groups have similar characteristicsFinding Data on ElementsEach square in the periodic table lists four pieces of information: an elements atomic number, chemical symbol, name, and atomic mass.

37Problems:The atomic number tells how many _________ are in an atom of the element.ProtonsProblems:What is the chemical symbol for lead?PbProblems:How many protons does potassium have?19Problems:What group number is beryllium in?Group 2Problems:What period does silver belong to?Period 5Notes 4-5Radioactive ElementsIsotopesAtoms with same number of protons but different numbers of neutronsExample:Carbon-12 (normal carbon) versus Carbon-14Some isotopes are unstableNuclei break down in a process of radioactive decay, releasing particles and energyRadioactivitySpontaneously emitting radiationExample: Uranium, Polonium, Radium

There are 3 types of radioactive decayTypes of Radioactive DecayDuring alpha decay, a nucleus loses an alpha particle, which consists of two protons and two neutrons.

* Decreases atomic # by 2, and mass # by 446

Types of Radioactive DecayDuring beta decay, a neutron inside an unstable nucleus changes into a negatively charged beta particle and a proton.

* Atomic # increases by 1, mass # remains the same47Types of Radioactive DecayGamma radiation has no charge and does not cause a change in either the atomic mass or the atomic number.

48Types of Radioactive DecayThe three types of nuclear radiation were named based on how easily each one could be blocked. Alpha, beta, and gamma are the first three letters of the Greek alphabet.

49Using Radioactive IsotopesCancer treatmentChemical reactionsIndustrial processesElectricitySmoke detectorsPest controlRock/ fossil datingFood treatmentNuclear weapons

Risks of Radioactive IsotopesBurn causingCancer causingGenetic mutationsdeath

ReviewUse your periodic table to predict the element that forms in each case of radioactive decay:IsotopeType of DecayElement FormedUranium-238AlphaNickel-63BetaIodine-131BetaRadium-226AlphaThorium-234Copper-63Xenon-131Radon-222