Basic Chemistry CHAPTER 2-2

Radioisotopes  Heavier isotopes that are unstable and tend to decompose to become more stable

Radioactivity  Radioactivity—process of spontaneous atomic decay  What can we use this for?

Radioactivity  But how does this happen?

Radioactivity  But how does this happen?  nuclei are unstable so dissipate excess energy by emitting radiation in alpha, beta, or gamma rays

Radioactivity  Radiometric Dating:  Uranium  238 U to 206 Pb, with a half-life of 4.47 billion years  235 U to 207 Pb, with a half-life of 704 million years.  Carbon  Carbon-14 is a radioactive isotope of carbon, with a half- life of 5,730 years  Very short compared to other isotopes

Radioactivity  PhET Simulation 

Inert Elements  Atoms are stable (inert) when the outermost shell is complete

Inert Elements  Atoms are stable (inert) when the outermost shell is complete  Atoms will gain, lose, or share electrons to complete their outermost orbitals and reach a stable state

Inert Elements  Atoms are stable (inert) when the outermost shell is complete  Atoms will gain, lose, or share electrons to complete their outermost orbitals and reach a stable state  Atoms are considered stable when their outermost orbital has 8 electrons (With exception to the first shell

Inert Elements

Reactive Elements  Valence shells are not full and are unstable  Tend to gain, lose, or share electrons  Allow for bond formation, which produces stable valence

Molecules and Compounds  Molecule: Two or more like atoms combined chemically  Compound: Two or more different atoms combined chemically

Molecules and Compounds

What are chemical reactions?  What do you remember?

What are chemical reactions?  Atoms are united by chemical bonds OR  Atoms dissociate from other atoms when chemical bonds are broken

Chemical Bonds  Ionic vs. Covalent  GSSV466Gk

Ionic Bonds  Form when electrons are completely transferred from one atom to another  Ions  Charged particles  Anions - negative  Cations - positive  Either donate or accept electrons

Ionic Bonds +– Sodium atom (Na) (11p + ; 12n 0 ; 11e – ) Chlorine atom (Cl) (17p + ; 18n 0 ; 17e – ) Sodium ion (Na + )Chloride ion (Cl – ) Sodium chloride (NaCl) ClNaCl Na

Covalent Bonds  Atoms become stable through shared electrons  Single covalent bonds share one pair of electrons  Double covalent bonds share two pairs of electrons

Covalent Bonds - Example

Covalent vs. Ionic bonds

Covalent vs. Ionic bonds

Polarity  Covalently bonded molecules

Polarity  Some are non-polar  Electrically neutral as a molecule  Some are polar  Have a positive and negative side

Polarity  ecule-polarity

Hydrogen bonds  Weak chemical bonds  Hydrogen is attracted to the negative portion of polar molecule  Provides attraction between molecules

Hydrogen bonds

 How many drops of water can you fit on a penny?  Who can guess correctly??