Chem - Lecture 3 Flashcards
Structure of the atom – \_\_\_\_\_\_ – Determines mass of atom • \_\_\_\_\_\_ – Positive – Determines element • \_\_\_\_\_\_ – Neutral – Determines isotope
Structure of the atom – Nucleus – Determines mass of atom • Proton – Positive – Determines element • Neutron – Neutral – Determines isotope
Atomic Mass • Atoms are tiny, we need units that are useful for describing the… – … mass of a single atom • \_\_\_\_\_\_ \_\_\_\_\_\_ \_\_\_\_\_\_( \_\_) – … number of atoms in a given sample • \_\_\_\_ (mol)
Atomic Mass
• Atoms are tiny, we need units that are useful for describing the…
– … mass of a single atom
• Atomic Mass Units (amu) – … number of atoms in a
given sample
• Mole (mol)
Measuring Atoms and 12C
• Definition 1
- A single carbon-12 atom has a mass of exactly 12amu 1 amu = (1/12) mass of 12C nucleus
- It’s a tiny mass, for our tiny atoms
Measuring Atoms and 12C
• Definition 1
- A single carbon-12 atom has a mass of exactly 12amu 1 amu = (1/12) mass of 12C nucleus
- It’s a tiny mass, for our tiny atoms
Measuring Atoms and 12C
• Definition 2
• Exactly 12g of carbon-12 contains exactly 1 mole of atoms 6.022 x 1023 (Avogadro’s number)
• A large number, so we can count all of our tiny atoms
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Measuring Atoms and 12C
• Definition 2
• Exactly 12g of carbon-12 contains exactly 1 mole of atoms 6.022 x 1023 (Avogadro’s number)
• A large number, so we can count all of our tiny atoms
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Measuring Atoms Example
• Now, we can provide a single number and it will convey two meanings
– The mass of a single ______
– The mass of a mole of that ______ 6.022 x 1023 ______ atoms
Measuring Atoms Example
• Now, we can provide a single number and it will convey two meanings
– The mass of a single isotope – The mass of a mole of that isotope 6.022 x 1023 isotope atoms
Average Atomic Mass
• Each isotope has a natural abundance
• Some isotopes are rare, while others are common
» ______
• Abundances are similar world-wide
» Are abundances similar world-wide?! (Answer: ______ ______)
Average Atomic Mass
• Each isotope has a natural abundance
• Some isotopes are rare, while others are common
» True
• Abundances are similar world-wide
» Are abundances similar world-wide?! (Answer: close enough)
Average Atomic Mass
• The periodic table provides the average mass, weighted by isotopic abundance
– Goal: To know how many atoms are in a sample just by kn
– Plain English:
• You multiply how heavy an ______ is with how ______it is, then add up all the ______
– Math/technical
• Take the product of ______ and ____ for every ______, take the sum of those products over all naturally occurring ______
Average Atomic Mass
• The periodic table provides the average mass, weighted by isotopic abundance
– Goal: To know how many atoms are in a sample just by kn
– Plain English:
• You multiply how heavy an isotope is with how abundant it is, then add up all the numbers
– Math/technical
• Take the product of frequency and mass for every isotope, take the sum of those products over all naturally occurring isotopes
Periodic Table
• ______ are arranged by atomic number
– Number of ______
• Magnitude of positive charge in the______
• Rows are called “______” • Columns are called “______”
– ______ in the same column have similar properties
Periodic Table
• Elements are arranged by atomic number
– Number of protons
• Magnitude of positive charge in the nucleus
• Rows are called “periods” • Columns are called “groups” – Elements in the same column have similar properties
The Chemical Bond
• Sometimes atoms stick together to form a new ______
– Example: two hydrogen atoms will react to spontaneously form __ (molecular hydrogen)
• Separation distance between nuclei ≈ 0.8 Å
The Chemical Bond
• Sometimes atoms stick together to form a new compound
– Example: two hydrogen atoms will react to spontaneously form H2 (molecular hydrogen)
• Separation distance between nuclei ≈ 0.8 Å
The Chemical Bond
• Remember:
– Like charges ______, opposite charges ______
• Let’s build up our H2 molecule:
- Start by adding the nuclei (0.8 Å apart)
• How do these two nuclei interact? - Add an electron to the system
• How will the nuclei interact with the electron?
The Chemical Bond
• Remember:
– Like charges repel, opposite charges attract
• Let’s build up our H2 molecule:
- Start by adding the ______ (0.8 Å apart)
• How do these two ______ interact? - Add an ______to the system
• How will the nuclei interact with the ______?
The Chemical Bond
• Electron ______ between the nuclei pulls the nuclei together
– ______ region
• Electron ______ on either far edge of the nuclei will pull the nuclei apart
– ____________ region
The Chemical Bond
• Electron density between the nuclei pulls the nuclei together
– Binding region
• Electron density on either far edge of the nuclei will pull the nuclei apart
– Antibinding region
Ionic vs Covalent
• Ionic and covalent ______ are concepts that allow us to quickly predict how different ______ distribute ______ in the ______ region
Ionic vs Covalent
• Ionic and covalent bonds are concepts that allow us to quickly predict how different compounds distribute electrons in the binding region
What is the ionic concept
– One atom (metal) donates electron(s) to another atom (nonmetal)
• The nonmetal holds-on to the charge while the now positive metal atom is attracted to the nonmetal’s overall negative charge
What is the covalent concept
– Two atoms (nonmetals) share electrons roughly equally
• You’ll have to wait until Ch 9 and 10 to predict when/why you get a covalent bond
Ionic Compounds
• Composed of ______ and ______
• Often singly charged atoms, but some ______ ions do exist
– ______ = positive thing
• Often a ______ (almost always)
– ______ = negative thing
• Often/always ______ atom(s)
Ionic Compounds
• Composed of cations and anions
• Often singly charged atoms, but some polyatomic ions do exist
– Cation = positive thing
• Often a metal (almost always)
– Anion = negative thing
• Often/always nonmetal atom(s)
