To her chemistry professor at West Chester University, she was the well-prepared junior from Philadelphia who, in class three nights ago, "was really engaged and following this discussion of how nanoparticles grow into raindrops."

And now, to Philadelphia police, Selene K. Raynor, 21, is the 241st homicide of the year, a victim of a boyfriend with a troubled past and a semiautomatic pistol.

Raynor was pregnant. Police say Tyrell Hart, 19, quarreled with her Wednesday night, shot her in the head, went home, took a shower, and went to sleep.

"From all accounts, she was a very nice young lady," Philadelphia Police Capt. James Clark said. "It just seemed like she got hooked up with the wrong guy."

Hart, 19, was charged yesterday with killing Raynor and her unborn child. It was not known if he was the child's father.

Police say the killing occurred just hours after Raynor's evening chemistry class at West Chester.

Raynor had been dating Hart for a short period and picked him up Wednesday night from his home in the 3000 block of Clifford Street in the Strawberry Mansion section, police said.

The two drove to the 1900 block of North Newkirk Street, a few blocks from Hart's home, and parked "to talk about some aspect of their relationship," Clark said.

Police said that at some point, Hart pulled out a gun and shot Raynor once in the head.

Raynor's mother began calling police soon after she realized her daughter was missing, police said. About 1 p.m. Thursday, someone in Strawberry Mansion saw a body inside a silver Jeep and called police.

The Jeep, registered to Raynor's mother, was the vehicle Raynor drove to Hart's home, Clark said.

Authorities were led to Hart quickly, Clark said, after someone reported last seeing Raynor with Hart. Clark would not elaborate except to say police had recovered the alleged murder weapon from someone else.

Clark said Hart was "known" to police. Court records show he is scheduled to stand trial in January with another man on a Philadelphia drug charge, in a case that has been postponed three times since April. Hart's lawyer, Jeffrey Azzarano, could not be reached for comment last night.

Yesterday, Raynor's classmates and instructors at West Chester and Philadelphia High School for Girls, from which she graduated in 2006, were grieving.

Erimar Hernandez, a senior who is majoring in social work at La Salle University, said she had had many classes with Raynor in high school.

"She was really friendly and outgoing, got along with mainly everyone," Hernandez said.

Another high school classmate, Rachel LaPorte, also a senior social-work major at La Salle, agreed.

"She was a very upbeat, happy person," said LaPorte, adding that Raynor was always telling jokes that "would crack us all up. She would go out of her way to make someone smile or laugh."

At college, Raynor was active in campus life, including the Gospel Choir, Black Student Union, and Student Activities Council.

Kurt Kolasinski, Raynor's chemistry professor and adviser for three years, said Raynor was always prepared for her advising sessions.

"She seemed like she had a plan and a purpose," Kolasinski said yesterday. "She was the type of person who made you feel better after you talked to her."

On her Facebook page, Raynor said she liked white pizza, Pepsi, and Twizzlers, listed her goal as "running my own dental office," and identified "being around my entire family" as the best feeling in the world. Her family, she said, included her mother and sister.

"Selene was a special young lady who touched the lives of many on campus," said a statement from Pam Sheridan, a West Chester University spokeswoman.

Raynor was commuting to college this semester. Before, she had lived on campus and served as a resident assistant in Sanderson Hall, Sheridan said. In her resident assistant's profile posted online, Raynor said her favorite vacation spot was "anywhere far from Philly."

A quiz on her Facebook page asks: "How do you want to die?" Raynor's answer: "Old."

About 300 people attended an impromptu vigil for Raynor on Thursday evening at the university, Sheridan said. "We paid a wonderful tribute to her," said Grace Hackett Kelly, the longtime adviser to the Gospel Choir. She described Raynor as "very outgoing, full of life."

"There's a huge void in the choir - and on the campus," said Kelly. "She loved the Lord, and now she's going to be with him."

Staff writer Olivia Biagi contributed to this article.