1. Chapter 2.1 Atoms, Ions, and Molecules
INB Pg 12

2. Vocabulary Atom Element Compound Ion Cation Anion Ionic bond
Covalent bond
molecule

3. Chemistry: Why Does it Matter?
All organisms depend on many chemicals and chemical reactions to make life possible

4. Atoms
Every physical thing you can think of, living or nonliving, is made of incredibly small particles called atoms
An atom is the smallest basic unit of matter

5. Atoms All atoms share the same basic structure
Protons: positively charged, found in the nucleus (center) of an atom
Neutrons: no charge (neutral), found in the nucleus (center) of an atom
Electrons: negatively charged, found orbiting the nucleus

6. Atoms

7. Atoms and Elements
An element is one particular type of atoms, and it cannot be broken down into simpler substances by ordinary chemical means
Ex: Oxygen, hydrogen, carbon, gold

8. Electrons
The properties of elements are determined by the number of electrons
Electrons orbit the nucleus in regions called energy levels
Atoms are most stable (happy) when they have full energy levels

9. Elements
Of the 91 elements that naturally occur on Earth, only about 25 are found in organisms
Just four elements – carbon (C), oxygen (O), nitrogen (N), and hydrogen (H)- make up 96% of a human body’s mass
Other 4%: calcium (Ca), phosphorus (P), potassium (K), sulfur (S), sodium (Na), and other trace elements

10. Compounds
The atoms of elements found in organisms are often linked, or bonded, to other atoms
A compound is a substance made of atoms of different elements bonded together in a certain ratio
Ex: H2O (water)

11. Compounds
The properties of a compound are different than the properties of the individual elements that make up a compound
Sodium (Na) Chlorine (Cl) Sodium chloride (NaCl)
(purple/silver (poisonous yellow (table salt)
soft metal) gas)

12. Check Your Understanding
How are elements different from compounds?

13. Ions An ion is an atoms that has gained or lost one or more electrons
Gain electrons: negative ion (anion)
Lose electrons: positive ion (cation)
Atoms gain/lose electrons to fill their energy levels

14. Ions
The type of ion that is formed depends on the number of electrons in the outermost energy level
These electrons are called valence electrons
An atom with few valence electrons will lose ions to form cations
An atom with almost full outer energy level will gain electrons to form anions

16. Check Your Understanding
Sodium (Na) atoms have 1 valence electron. Are sodium atoms more likely to form positive ions (cations) or negative ions (anions)?
(Remember, electrons are negative, so atoms that lose electrons are losing a negative charge and therefore becoming more positive. Atoms that gain electrons are gaining a negative charge and becoming more negative)

17. Ions
Ions are usually formed when electrons are transferred from one atom to another
Ions that have opposite charges (such as Na+ and Cl-) are attracted to one another and will form an ionic bond (a bond between two oppositely charged ions)

18. Check Your Understanding
What determines whether an atom becomes a positive ion or a negative ion?

19. Covalent Bonds Not all atoms can lose or gain electrons easily
Sometimes, atoms of many elements share pairs of electrons to fill their outer shells
A covalent bond forms when atoms share a pair of electrons

20. Covalent Bonds
Covalent bonds are generally very strong, and often two atoms may form several covalent bonds to share multiple pairs of electrons

21. Check Your Understanding
What is the difference between a covalent bond and an ionic bond?

22. Covalent bonds
A molecule is two or more atoms held together by covalent bonds
Some elements occur naturally as molecules (called diatomic molecules)
Ex: oxygen as O2

23. Check Your Understanding
What happens to electrons in the outer energy levels when two atoms form a covalent bond?