The Structure of Atoms The Basic Building Block of Ma8er (TEKS 8.5A) The ParAcle Theory of Ma8er •  Ma8er is made of parAcles that are in constant moAon •  Every kind of ma8er is made of one or more elements •  Atoms are the smallest parAcle of an element Elements •  Elements are the building blocks of all ma8er •  The periodic table is a list of all of the elements that can build ma8er. •  It is a graphic organizer of chemistry Elements •  There are currently 118 elements that have been idenAfied though only 88 of them are naturally occurring. Atomic Number, Weight and Mass •  Atomic Number: # of protons in an atom’s nucleus. •  Atomic Weight: the average mass of an atom of an element (in amu); an averaged figure •  Atomic Mass: the mass of one atom of that element Hydrogen. Atomic
number
Elemental
symbol
Atomic
Mass
number
Element
name
1 H 1.008 Hydrogen Draw this in miniature on your page! A Quick Review of the Structure of Atoms Subatomic ParAcles •  There are three basic parts of an atom: –  Protons = posiAve –  Neutrons = no charge –  Electrons = negaAve PROTON
•  Positive Charge
•  Located INSIDE the
NUCLEUS
•  Weight of 1 AMU
• AMU= Atomic Mass Unit
• Protons determine an
element’s identity
Neutron
Not this neutron….
•  Neutrons have a NEUTRAL
charge
•  They are located INSIDE the
Nucleus
•  They weigh 1 AMU (atomic
mass unit)
Electron
•  Electrons have a NEGATIVE
charge
•  They are located OUTSIDE
the nucleus on energy levels/
shells
•  Electrons have almost no
weight.
1/1836 the size of
a proton.
•  Electrons are not counted
when weighing an atom.
Atomic Structure •  Atoms are composed of 2 regions: –  Nucleus: the center of the atom that contains the mass of the atom –  Electron cloud: region that surrounds the nucleus that contains most of the space in the atom Electron
Cloud
Nucleus
What’s in the Nucleus? •  The nucleus contains 2 of the 3 subatomic parAcles: –  Protons: posiAvely charged subatomic parAcles –  Neutrons: neutrally charged subatomic parAcles What’s in the Electron Cloud? •  The 3rd subatomic parAcle is found in a cloud that surrounds the nucleus of an atom –  Electron: the subatomic parAcle with a negaAve charge and relaAvely no mass Electrons and Mass •  The mass of an electron is so small compared to protons and neutrons that it has li8le effect on the overall mass of an atom. How do the subatomic parAcles balance each other? •  In an atom: – The number of protons = the number of electrons •  If 20 protons are present in an atom then 20 electrons are there to balance the overall charge of the atom — atoms are neutral – The neutrons have no charge; therefore they do not have to equal the number of protons or electrons How do these parAcles interact? •  Protons and neutrons live compacted in the Any posiAvely charged nucleus accounAng for most of the mass of the atom •  The negaAvely charged electrons are small and have a REALLY small mass but occupy a large volume of space outside the nucleus Space outside the nucleus: •  Electrons live in something called shells or energy levels •  Only so many can be in any certain shell •  The electrons in the outer most shell of any element are called valence electrons Valence electron
ATOMIC STRUCTURE Electrons are arranged in Energy Levels or Shells around the nucleus of an atom. • 
first shell a maximum of 2 electrons •  second shell
a maximum of 8 electrons •  third shell a maximum of 18 electrons Where are “shells”? Valence Electrons •  The electrons farthest away from the
nucleus are called valence electrons
–  They affect the way an atom bonds
–  Atoms can have anywhere between 1 and 8
valence electrons
–  Valence electrons determine an element’s
chemical properties, including reactivity
–  These electrons are shown in models in an
arrangement known as the “electron cloud”
Electron Cloud Model •  The current model scienAsts use •  It shows the electrons as forming a negaAvely charged cloud around the nucleus •  It is impossible to determine exactly where an electron is at any given Ame •  MYTH – electrons DO NOT orbit the nucleus like planets orbit the sun! SUMMARY
1.  The Atomic Number of an atom = number of protons in the nucleus. 2.  The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. 3.  The number of Protons = Number of Electrons. 4.  Electrons orbit the nucleus in shells. 5.  Each shell can only carry a set number of electrons. Neils Bohr •  In 1913, Bohr proposed a theory about the structure of the atom based on Rutherford's theory •  Rutherford believed that the atom consisted of a posiAvely charged nucleus, with negaAvely charged electrons in orbit around it. (Remember the video you watched?) •  Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. •  He said that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properAes. Bohr Model •  The Bohr Model shows all of the parAcles in the atom •  In the center is circles. Each circle represents a single neutron or proton. Protons should have a plus or P wri8en on them. Neutrons should be blank or have an N •  In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e -
+
+
-
The Rule of 8
•  All atoms want to have a full valence shell -­‐ 8 electrons –  This makes for happy atoms that will not react with other atoms. •  Atoms with less than 8 electrons in their valence shell will react chemically (bond) with other atoms in one of 2 ways: –  Gain electrons to equal 8 –  Lose their valence electrons •  In general, the fewer the electrons that need to be gained or lost, the easier and faster the atom will react Bohr models
Aluminum - Al
Sodium - Na
Making a Bohr Model of the Atom Find this page: 1.  Use this page to help you make the models – the models you are doing are on the back. 2.  Make the models, take pictures and fill in the informaAon on the page. 3.  The front side and whatever you do not finish in class is HW Purpose and Materials: Purpose: To understand and describe the Bohr model of the atom using the Periodic Table and food! Materials: periodic table, cups of round candy or cereal, bohr model diagram page, camera/
phone. Procedure: 1.  Use your PT (in journal) to determine the symbol and other informaAon about each element. (hint: # of N = atomic mass -­‐ # P) 2.  Fill in the missing informaAon into the “squares”. Do this for each element -­‐ BEFORE using the food! 3.  You are filling in the BACK of the page (you may work on the FRONT when we are done making models and your space is clean) Procedures (cont’d) 4. Pick out 3 colors of candy/cereal to represent protons, neutrons and electrons. Make a quick key on your page 4. To represent P, N, E with the food on each model, place the candies where they need to be on the page. 5. Take a picture of your models with your phone! Bohr model page: PracAce -­‐ let’s do one together! 1.  Sulfur, let’s fill in the square. 2.  How many protons does it have? How many neutrons? 3.  How many electrons? 4.  Be sure to put P and N in the nucleus and E on the ring(s) Sulfur With your partner 1.  Now complete the rest of the page with your partner. Make sure to stay with the color key that you have made. 2.  BEFORE you take a picture, your models need to be checked. 3.  Invite another group to see your models. Explain them to that group. If they do not agree with your explanaAon, revisit your model. 4.  If it’s good -­‐ take those pictures!! Cheat Sheet! •  To find the numbers: 1.  Atomic # = # of P 2.  # of electrons = # of P 3.  To find neutrons: Mass # = P + N So N = mass # -­‐ P HW: Remember: The front side and whatever you do not finish in class is HW There will also be a short quiz on Wednesday on the structure of atoms