Unit 3: Atomic Structure Sections 1-2

warmup All matter is composed of very small particles called atoms. In middle school science you learned about the atom. 1. Draw a picture of a typical atom. Identify and label the location of the nucleus, electrons, neutrons, protons.

Objective Sections 1-2  I can summarize Dalton's theories.  I can describe properties of protons, neutrons and electrons, who discovered them and where they are found in an atom.

Section 1 What is an atom? Describe it’s size  Definition: The atom is the smallest particle of an element that retains the characteristics of that element.  A typical atom is meters across -- that's one billionth of a meter Video: Just how small is an atom 5:20

What is an atom? A. An atom is the smallest particle that can exist B. An atom is the smallest particle that still has characteristics of an element C. An atom is a solid sphere, like a marble only really really small

Section 1 Dalton’s 4 Postulates (1808) 1. All elements are composed of tiny indivisible particles called atoms 2. Atoms of the same element are identical. Atoms of different elements are different from another element. 3. Atoms of different elements can chemically combine to form compounds 4. Any chemical reaction is simply a re-arrangement of atoms, but the atoms are not changed into different elements. John Dalton “Father of Modern Chemistry”

Section 2 Structure of the atom  Electrons  Discovered by J.J. Thomson in Sir Joseph John Thomson ( ) Nobel Prize for Physics (1906) Discovered the electron First to discover evidence for isotopes of stable elements.

Section 2 Structure of the atom  Thomson created and used a Cathode Ray Tube to study the existence of electrons.  He passed an electric current through a sealed vacuum. Negatively charged electrons are repelled by the negatively charge cathode, and are attracted to the positively charged anode causing a glowing cathode ray to appear Thomson - determined the presence of these electrons in all gases and concluded that electrons were part of all atoms

Section 2 The Atomic Nucleus  In Thomson’s “Plum Pudding Model”: Scientists assumed the negative electrons were evenly distributed throughout a positive atom.

Which of Dalton’s four theories did J.J. Thomson disprove in his famous CRT experiment? A. All elements are composed of tiny indivisible particles called atoms B. Atoms of the same element are identical. Atoms of different elements are different from another element. C. Atoms of different elements can chemically combine to form compounds D. Any chemical reaction is simply a re-arrangement of atoms, but the atoms are not changed into different elements.

Section 2 Structure of the atom  Robert Millikan - experimented to find the relative electrical charge of an electron to be –1  Millikan discovered electron mass to be 1/1840 of the mass of a hydrogen proton  Electrons in an atom determine its chemical properties Robert Millikan Nobel Prize for Physics 1923 first measured the electron charge and mass

Section 2 Structure of the atom  Protons  Since atoms are electrically neutral, there must be a particle that neutralizes the negative charge of an electron  Protons were discovered by Eugen Goldstein in 1886 who observed additional rays in a cathode ray tube that traveled in the opposite direction of the cathode ray.  Protons have a electrical charge of +1 and a mass of 1 amu.  The number of protons in an atom determines the type of element Eugen Goldstein discoverer of the proton

Section 2 Structure of the atom  Neutrons  James Chadwick discovered the existence of neutrons in 1932 using beryllium, alpha rays and known atomic masses.  Neutrons hold the protons together and thus contribute to the stability of the atomic nucleus.  Neutrons have a mass of 1 and no electric charge. James Chadwick Nobel Prize for Physics 1935

It has a very small mass, and a negative charge. What is it and where is it located in the atom? A. A Neutron is located outside the nucleus B. A Proton located in the nucleus C. An Electron is located in the nucleus D. An Electron is located in the electron cloud outside the nucleus.

Section 2 Structure of the atom  In 1909 Ernest Rutherford disproves the plum pudding model by bombarding gold foil with alpha particles(+). Ernest Rutherford Nobel Prize for Chemistry 1908

Section 2 Structure of the atom  According to the Thomson’s popular “Plum Pudding” atomic theory of the time, the alpha particles should pass through the foil with only a slight deflection  Instead, Rutherford observed that almost all particles went straight thru, but a few of the particles were deflected at odd angles or sometimes directly backwards!!  This result was completely unexpected. Gold Atom

Section 2 Rutherford’s planetary model  Rutherford uses this information to propose a new atomic theory.  The atom is mostly made up of empty space.  The positive charge of the atom, and most of the mass, is concentrated in a small area  This small, dense area is known as the nucleus, and is surrounded by orbiting electrons.

Section 2 Rutherford’s Experiment   Animations  Cathode Ray Tube  Alpha Particle Scattering …Rutherford’s experiment  = Alpha Particle 2 protons + 2 neutrons

In his famous gold foil experiment, Rutherford shot alpha particles into gold. What result did he prove? A. Atoms have a large diffuse nucleus, like a pudding. B. Atoms are made up of mostly empty space C. Atoms have a small dense positively charged nucleus D. The nucleus is actually much smaller and more dense than anyone knew

Atom Facts ElectronProtonNeutron Charge+10 Mass 1/1840 (almost negligible) 1 amu Location in Atomelectron cloudnucleus DiscovererJ.J. ThomsonGoldstein James Chadwick Function determines chemical properties determines an elements identity holds nucleus together

Atom Facts ElectronProtonNeutron Charge+10 Mass 1/1840 (almost negligible) 1 amu Location in Atomelectron cloudnucleus DiscovererJ.J. ThomsonGoldstein James Chadwick Function determines chemical properties determines an elements identity holds nucleus together

Objective Sections 1-2  To Summarize Dalton’s atomic theory  Describe size of an atom  Distinguish among protons, electrons and neutrons in terms of relative mass, charge, location and function  Who Discovered…..  the electron?J.J. Thomson  the proton?Eugen Goldstein  the neutron?James Chadwick

Distinguishing between atoms Atomic Number Section 3 Atomic Number

Atom Facts Review ElectronProtonNeutron Charge+10 Mass 1/1840 (almost negligible) 1 amu Location in Atomelectron cloudnucleus DiscovererJ.J. ThomsonGoldstein James Chadwick Function determines chemical properties determines an elements identity holds nucleus together

Objective Section 3  I can distinguish atoms of different elements and between isotopes and how to name them  Distinguish 1. atomic number, 2. mass number 3. atomic mass.  I can calculate atomic mass

Section 3 Atomic number  The atomic number of an atom is equal to the number of protons in an atom  It is also equal to the number of electrons in a neutral atom  Why would the number of protons and electrons need to be the same in an atom?

Mass Number  The mass of an atom is concentrated in the nucleus and is made up of protons and neutrons  An atom’s mass number is the total number of protons and neutrons in its nucleus.  i.e. Mass # = protons + neutrons  The number of neutrons in an atom can be determined by a quick calculation:  Number of neutrons = mass number – atomic number

What is the mass number of an atom of Beryllium that has 5 neutrons? A. 4 B. 5 C. 8 D. 9 Mass # = protons + neutrons

An atom of Titanium has 22 protons and has a mass number of 48. How many neutrons are in this atom? A. 22 B. 25 C. 26 D. 70 Mass # = protons + neutrons

The composition of an atom is given in the following shorthand: N 15 7 Protons = ______ Neutrons = ______ Electrons = ______

What element is this? A. calcium B. chlorine C. carbon D. carbonite

What is the atomic number?

What is the mass number?

How many neutrons in this atom?

Isotopes  Remember! Neutrons in an atom hold the nucleus together and make it stable.  An isotope of an element is an atom of that element with the normal number of protons, but a different number of neutrons.  Isotopes are chemically alike because they have the same number of protons and electrons, but differ slightly from Dalton’s atomic theory since the number of neutrons may differ.  Isotopes are also named using the element’s name followed by the number of protons + neutrons.  example: Carbon-14

Isotopes Isotopes of Carbon ProtonsElectronsNeutronsName 667 Carbon Carbon Carbon-15

Isotopes  Some highly unstable isotopes can be useful:  Carbon – 14: half life: 5730 years  archaeological carbon dating  Iodine – 131: half life: 8.02 days  treatment of thyroid disorders  Americium – 241: half life: years  smoke detectors

Which of Dalton’s four theories was disproven by the discovery that elements have isotopes with differing neutrons? A. All elements are composed of tiny indivisible particles called atoms B. Atoms of the same element are identical. Atoms of different elements are different from another element. C. Atoms of different elements can chemically combine to form compounds D. Any chemical reaction is simply a re-arrangement of atoms, but the atoms are not changed into different elements.

How to calculate Atomic Mass  Most elements have more than one stable isotope as you find them in nature.  Definition: Atomic Mass the weighted average of the masses of the isotopes of an element.  Some isotopes occur more often than others so the atomic mass of an element is the average of the isotopes’ mass weighted by the abundance of that isotope.  To calculate an element’s atomic mass, you need to know  the number of stable isotopes that exist for that element,  the mass of each isotope, and  the percent abundance of that isotope.

How to calculate Atomic Mass  Example: in any sample of the element neon that you find, there are three isotopes present.  Most of it, 90.48%, is neon amu 0.27% is neon amu 9.25% is neon amu  To calculate the average atomic mass multiply the mass of each isotope by its %abundance and add them together. Neon-20: x.9048= Neon-21:20.993x.0027= Neon-22:21.991x.0925= Atomic mass of neon is amu  Try it this way on your calculator:  x x x.0925 [enter]

Practice 1 In any piece of copper you may find there are two naturally occurring isotopes: Copper-63 (29 protons and 34 neutrons) and Copper-65 (29 protons and 36 neutrons) Copper-63 weighs amu and is 69.2% abundant Copper-65 weighs amu and is 30.8% abundant Calculate the atomic mass of Copper. Round to 2 decimal places, Enter numeric answer key for the. decimal point

Bromine has two naturally occurring isotopes. Calculate the atomic mass Br = amu (50.69% abundant) Br = amu (49.31% abundant) Round to 2 decimal places, Enter numeric answer key for the. decimal point

Section 4 the Periodic Table How it came about? Location, location, location!!!

Objective Section 4  I can describe the origin of the periodic table  Identify the position of key groups, periods and the metals, nonmetals, in the periodic table

Warm up Questions  An atom has an atomic number of 4 and a mass number of How many protons, electrons and neutrons does this atom have? 2. What element is this atom? 3. How would you write the name of this isotope?  An atom of aluminum has a mass number of How many protons, electrons and neutrons does this atom have 2. How would you write the name of this isotope of aluminum?

Section 4 – Development of the periodic table Dmitri Mendeleev A.Dmitri Mendeleev  Mendeleev was the first scientist who tried to organize the elements into a logical pattern.  In 1869, he first listed elements in columns in order of increasing atomic mass.  That arrangement didn’t show any logical trends, so he arranged columns with elements that have similar properties side by side in a table. (p123)  Using this table, he actually predicted the properties of elements yet to be discovered!!!! Dmitri Mendeleev ( )

Section 4 – Development of the periodic table Henry Moseley  Henry Moseley then arranged the elements according to atomic number, keeping the conditions Mendeleev started with.  Moseley’s arrangement allows us to predict the physical and chemical properties of elements simply based on their location in the table. Henry Moseley

B.The Modern Periodic Table -- The Periods--  Mendeleev’s and Mosley’s discoveries give rise to Periodic Law  Horizontal rows are called periods. There are a total of 7 periods.  Periodic law: when the elements are arranged in order of atomic number, there is a repetition of physical and chemical properties. Periods go across …..

B.The Modern Periodic Table --- the groups  Vertical columns are called groups.  The elements in any group tend to have the same physical and chemicals properties. Groups go up & down

Groups are numbered and labeled with a letter. Group A elements called the representatives elements have a wide range of chemical and physical properties

There are three general classes of elements: 1. Metals solid at room temp., conduct electricity, ductile, malleable 2. Nonmetals usually non-lustrous, poor conductors of electricity, gases 3. Metalloids intermediate properties between metals and nonmetals

Stair Case divides metals from non-metals MetalsNon-Metals Metalloids

Significant groups Alkali metals Alkaline earth metals Transition Metals Halogens Nobel Gases

Group 1A: Alkali metals = H, Li, Na, K, Rb, Cs, Fr react violently with water react violently with water

Group 2A: Alkaline earth metals = Be, Mg, Ca, Sr, Ba, Ra Lustrous, Silvery, somewhat reactive

Transition Metals (Group B) all have similar metal properties: solid at room temp., conduct electricity, ductile, malleable

Group 7A: Halogens = F, Cl, Br, I, At are all nonmetals and are very reactive

Group 0 also called Group 8A Noble gases = He, Ne, Ar, Kr, Xe, Rn are all nonmetals and also known as inert gases because they have virtually no chemical reactivity.

Match the element to its group GroupsMatch the property to its group 1. ____ CesiumA. halogen6. ___ no reactivity 2. ____ FeB. noble gas7. ___ silvery, somewhat reactive 3. ____ SrC. alkali metal8. ___ all have similar metal properties 4. ____ NeonD. transition metal9. ___ very reactive non-metals 5.___ BrE. alkaline earth metal10. ___ react violently with water Quiz yourself!

Match the element to its group GroupsMatch the property to its group 1. _C__ CesiumA. halogen6. _B_ no reactivity 2. _D__ FeB. noble gas7. _E_ silvery, somewhat reactive 3. _E__ SrC. alkali metal8. _D_ all have similar metal properties 4. _B__ NeonD. transition metal9. _A_ very reactive non-metals 5._A_ BrE. alkaline earth metal10. _C_ react violently with water Quiz yourself! answers!