Download September 22 Bellwork

September 22 Bellwork
What are the three subatomic particles and their
charges?
What is an Atom?
 The smallest particle of matter that still has all of the
properties and characteristics of that type of matter.
 A copper atom is the smallest particle of copper that
still has all properties of copper.
 Brownian motion – the perpetual movement of
particles (jiggling atoms) named after Robert Brown
(Scottish Botanist)
What Do Atoms Look Like?
 An atom is mostly empty space and contains what we
call subatomic particles. They are electrons, protons
and neutrons.
Subatomic Particles
 Protons with a positive charge found in the nucleus of
an atom
 Neutrons with a neutral charge also found in the
nucleus of an atom
 Electrons with a negative charge found outside of the
nucleus in the electron cloud
The Periodic Table
 The elements are arranged according to
characteristics in a grid-like structure, both how they
look as well as the way they act
 Each box represents an element and each box
contains the
 Atomic number (number of protons/electrons)
 Atomic mass number
 Chemical symbol
Atomic Number
 The smaller number with no decimals
 Represents the number of protons and electrons in a
neutral atom
 Periodic trend: increases from top to bottom and from
left to right
 Example: If the atomic number is 2, then the atom has
2 electrons and 2 protons.
 Example 2: K has _19_ protons and _19_ electrons
when neutral
Atomic Mass Number
 The larger number with a decimal
 Measured in amu (atomic mass units)
 Represents the number of protons and neutrons in an
atom
 Atomic Mass # = protons + neutrons
Therefore…
 To find the number of neutrons:
 Neutrons = mass number – atomic number
Example
Carbon has a mass number of 12.011
and an atomic number of 6.
How many protons does it have?
Chemical Symbol
 Single letters or first letter capitalized
 If there are 3 letters, it is a man-made element that
may get renamed
 Gold – Au (aurum)
 Iron – Fe (ferrum)
Any element with an atomic
number greater than 92 is manmade
Isotopes
 Atoms of the same element with the same number of
protons but different number of neutrons
 The mass number is an estimate of all of the possible
isotopes of each element
 Isotopes are the reason that there is usually a decimal
point in the atomic mass number
Example of an Isotope
 C-12 has 6 neutrons, C-14 has 8 neutrons
 C-12 is more often found in nature, so the atomic mass of C is 12.011
which is closer to 12 than 14
How the Periodic Table is Set
up
 Metals, Nonmetals, Metalloids
 Families (rows) and Periods (columns)
Metals
 Located to the left of the zigzag (except hydrogen
and metalloids)
 Properties:
 Luster (shine)
 Can be stretched and shaped
 Good conductors of heat/electricity
Nonmetals
 Located to the right of the zigzag
 Properties:
 Dull
 Poor conductors of heat/electricity
Metalloids/Semimetals/Semi-conductors
 Along the zigzag: B, Si, Ge, As, Te, Po
 Properties:
 Some are shiny but some are dull
 Not as good of conductors as metals but better than
nonmetals
Periods (Rows) and Families
(Columns)
 Rows/Periods
 Horizontal
 Elements in the same period don’t have the same
properties
 7 on the periodic table
Periods (Rows) and Families
(Columns)
 Columns/Families
 Also called groups
 Vertical
 Elements in the same group/family have common
properties
 18 on the periodic table
 Li, Na, K all have a similar chemical reaction with
water (H2O)
 They all create an explosion that releases hydrogen
gas (H2)
 Therefore, they are stored with oil, not water.
Valence Electrons
 The number of electrons in an atom’s outermost
energy level
 Elements in the same group/family have the same
number of valence electrons
 Atoms want to achieve a filled outermost energy level
 we call this an “octet” if the energy level contains 8
valence electrons
Each Family of Elements
Has its Own Name
 Alkali Metals
 Alkaline Earth Metals
 Transition Metals
 Halogens
 Noble Gases
Alkali Metals
 Group 1 elements (except H)
 Have 1 valence electron
 Are the most active metals
 Tend to react with group 7
elements (halogens)
Alkaline Earth Metals
 Group 2 elements
 Have 2 valence electrons
 Less reactive than alkali metals but still
reactive
 Tend to react with group 6
Transition Metals
 Groups 3-12 on periodic table
 Metals, but different from alkali
or alkaline earth metals
 Most have 1 or 2 valence e-s
 Include mercury (Hg) – the only
liquid metal at room temperature
Halogens
 Group 7 elements
 Some are gas, Br is liquid, and some are solid
 Have 7 valence e-s
 Tend to react with group 1 elements (alkali metals)
Noble Gases
 Group 8 elements
 Helium has 2 valence e-s
 Ne, Ar, Kr, Xe, Rn, all have 8 valence
e-s
 Are not reactive since they already
achieved an octet
 Make up less than 1% of earth’s
atmosphere
 Oxygen (21%), nitrogen (78%)
contribute to most of the atmosphere
Rare-Earth Elements
 Includes elements at bottom of periodic table (periods
6&7)
 First row = lanthanoid series (tend to be metals)
 Second row = actinoid series (most are man-made
and radioactive)
Names and Symbols of Commonly Used
Elements
 Aluminum (Al)
 Boron (B)
 Calcium (Ca)
 Carbon ( C )
 Chlorine (Cl)
 Copper (Cu)
 Helium (He)
 Hydrogen (H)
 Iron (Fe)
 Nitrogen (N)
 Oxygen (O)
 Sodium (Na)
 Gold (Au)
We Can Use the Periodic
Table to Draw Bohr Models
 A.k.a “planetary models”
 Protons, neutrons and electrons are represented in the
Bohr Model
 We know that protons and neutrons are located in the
nucleus at the center
 The electrons are located in the electron cloud in
energy levels
Energy Levels
 1st level holds a max of 2 e 2nd level holds a max of 8 e 3rd level also holds 18 e-
Lewis (Dot) Diagrams
 Electron dot diagrams are structures that show the
valence electrons as dots
 Valence electrons are the electrons in the outermost
shell and can be determined by looking at the group
number on the periodic table
 Groups 1A – 8A (SKIP TRANS. METALS)
If an element is in group 1A it
has 1 V.E.
If an element is in group 5A is
has 5 V.E.
Drawing Lewis Diagrams
To draw the diagram:
 Write the symbol down
 Place dots around the symbol, one on each side and
then begin to pair them
Ions and Isotopes
 Isotopes: atoms of the same element with
the same #p+ but different # of neutrons
 Mass Number: whole number; is only for one
isotope of an atom
 Atomic mass: has decimal places because it
is an average of the masses of all of the
isotopes
Ions
 An atom or molecule that has a charge.
 Loss of electrons  Positive charge (cation)
 Gain of electrons  Negative charge (anion)
What is different between
the 3 isotopes of hydrogen?
Isotopes
 Isotopes= atoms of the same element
that have the same atomic number but
different atomic masses due to a
different number of neutrons.
 Protons and neutrons have a relative
mass of 1, and electrons are 1/1840,
so electrons don’t really count when
determining the mass.
 •Since most of the mass of the element is from
protons and neutrons, changing the number of
neutrons changes the mass of the atom.
 •To determine the atomic mass, scientists take an
average mass of al isotopes of that atom. This gives
us decimal places.
Example of an Isotope
 Carbon-12 has a mass number of 12
 •How many protons does it have? Why?
 •How many electrons does it have? Why?
 •How many neutrons does it have? Why?
Example 2
 Carbon-14 has a mass number of 14
 •How many protons does it have? Why?
 •How many electrons does it have?
Why?
 •How many neutrons does it have?
Why?
 When scientists take the average of these
masses to determine the atomic mass, they
also consider which is more abundant
(common) in nature.
 C-12 is more often found in nature so the
atomic mass of C is 12.011, which is closer to
12 than 14.
What happens if we don’t have
the same number of protons
and electrons?
 Then we no longer have a neutral atom!
 –Neutral atoms have NO charge
 –They have the same number of positive particles as
negative particles. (They cancel each other out).
Neutral Atom
 Example:
 –Oxygen has an atomic number of 8.
 –An atom of oxygen has 8p+ and 8e –So
+8 + - 8 = 0
Ions
 In order for an atom to not be neutral,
the number of electrons changes but
the number of protons and neutrons
stays the same
 Ion – atom with either a positive or
negative charge (a charged particle)
Neutral vs ion atom
-2
O
 Protons = 8
 Protons = 8
 Neutrons = 8
 Neutrons = 8
 Electrons = 8
 Electrons = 10
Formula: electrons = protons – charge
e = 8 – (-2)
Write the ion as either O2- or O-2
Boron ion
 Protons =
 Electrons =
 Neutrons =
+3
B
 Formula: protons – charge = electrons
 If an atom has 7 protons and 10
electrons, what is its charge?
 •Negative ions are called ANIONS
 •Positive ions are called CATIONS
 Formula 1: Electrons = protons –charge
 Formula 2: Charge = protons – electrons
Atomic Mass Units (amu)
 Today it is possible to determine the
mass of an element using a mass
spectrometer.
 However, numbers are small and
impractical to work with. (i.e. Mass of F=
3.155 x 10 -23 g)
 It is easier to use relative masses of atoms
using a reference isotope as a standard.
Atomic Mass Units
 The reference isotope= Carbon 12. This isotope is
assigned a mass of exactly 12 amu.
 Atomic mass units= 1/12 of the mass of a Carbon-12
atom.
Atomic Mass
 In nature, most elements occur as a
mixture of two or more isotopes.
 Atomic mass= the weighted average
mass of the atoms in a naturally
occurring samples of the element.
Takes into account the relative
abundance
Atomic Mass
 To determine atomic mass, you must
know the number of isotopes, the mass
of each isotope and the percent
abundance of each isotope.
 Atomic mass = multiply the mass of each
isotopes by natural abundance and add
the products.
Atomic Mass of Carbon
 Example: Carbon has 2 isotopes: Carbon-12
which has a natural abundance of 98.89%
(0.9889) and Carbon-13 which has a natural
abundance of 1.11% (0.0111).
 Atomic Mass of carbon=
Atomic Mass of Magnesium
 Magnesium has three naturally occurring
isotopes. 78.70% of Magnesium atoms exist as
Magnesium-24 (23.9850 g/mol), 10.03% exist as
Magnesium-25 (24.9858 g/mol) and 11.17% exist
as Magnesium-26 (25.9826 g/mol). What is the
average atomic mass of Magnesium?
 Atomic Mass of Magnesium=
Atomic Mass of Lithium
 What is the average atomic mass of
Lithium if 7.42% exists as Li-6 (6.015 g/mol)
and 92.58% exists as Li-7 (7.016 g/mol)?
 Atomic Mass of Lithium=